`make check` fails under UBSan

[evverx]

https://github.com/evverx/avahi/actions/runs/19529919218/job/55910261731

+ cat test-suite.log
=======================================
   nss-mdns 0.15.1: ./test-suite.log
=======================================

# TOTAL: 1
# PASS:  0
# SKIP:  0
# XFAIL: 0
# FAIL:  1
# XPASS: 0
# ERROR: 0

.. contents:: :depth: 2

FAIL: check_util
================

Running suite(s): util
src/util.c:296:23: runtime error: applying zero offset to null pointer
    #0 0x55f8c9df9037 in buffer_init /home/runner/work/avahi/avahi/nss-mdns/src/util.c:296:23
    #1 0x55f8c9de49fd in test_null_buffer_zero_alloc_returns_nonnull_fn /home/runner/work/avahi/avahi/nss-mdns/tests/check_util.c:431:5
    #2 0x55f8c9dfc380 in srunner_run_tagged (/home/runner/work/avahi/avahi/nss-mdns/check_util+0x135380) (BuildId: ffc141223dec35154b6ef7a2a1dab40712b5c87d)
    #3 0x55f8c9ddd9f2 in main /home/runner/work/avahi/avahi/nss-mdns/tests/check_util.c:1057:5
    #4 0x7fdb8ce2a1c9 in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16
    #5 0x7fdb8ce2a28a in __libc_start_main csu/../csu/libc-start.c:360:3
    #6 0x55f8c9d045d4 in _start (/home/runner/work/avahi/avahi/nss-mdns/check_util+0x3d5d4) (BuildId: ffc141223dec35154b6ef7a2a1dab40712b5c87d)

SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior src/util.c:296:23 
src/util.c:296:23: runtime error: applying zero offset to null pointer
    #0 0x55f8c9df9037 in buffer_init /home/runner/work/avahi/avahi/nss-mdns/src/util.c:296:23
    #1 0x55f8c9de4f9d in test_null_buffer_nonzero_alloc_returns_null_fn /home/runner/work/avahi/avahi/nss-mdns/tests/check_util.c:459:5
    #2 0x55f8c9dfc380 in srunner_run_tagged (/home/runner/work/avahi/avahi/nss-mdns/check_util+0x135380) (BuildId: ffc141223dec35154b6ef7a2a1dab40712b5c87d)
    #3 0x55f8c9ddd9f2 in main /home/runner/work/avahi/avahi/nss-mdns/tests/check_util.c:1057:5
    #4 0x7fdb8ce2a1c9 in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16
    #5 0x7fdb8ce2a28a in __libc_start_main csu/../csu/libc-start.c:360:3
    #6 0x55f8c9d045d4 in _start (/home/runner/work/avahi/avahi/nss-mdns/check_util+0x3d5d4) (BuildId: ffc141223dec35154b6ef7a2a1dab40712b5c87d)

SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior src/util.c:296:23 
94%: Checks: 38, Failures: 0, Errors: 2
tests/check_util.c:70:P:verify_name:test_verify_name_allowed_minimal:0: Passed
tests/check_util.c:153:P:verify_name:test_verify_name_allowed_default:0: Passed
tests/check_util.c:115:P:verify_name:test_verify_name_allowed_empty:0: Passed
tests/check_util.c:189:P:verify_name:test_verify_name_allowed_wildcard:0: Passed
tests/check_util.c:230:P:verify_name:test_verify_name_allowed_too_long:0: Passed
tests/check_util.c:303:P:verify_name:test_verify_name_allowed_too_long2:0: Passed
tests/check_util.c:346:P:verify_name:test_verify_name_allowed_com_and_local:0: Passed
tests/check_util.c:361:P:ends_with:test_ends_with:0: Passed
tests/check_util.c:376:P:label_count:test_label_count:0: Passed
tests/check_util.c:387:P:buffer:test_buffer_alloc_too_large_returns_null:0: Passed
tests/check_util.c:397:P:buffer:test_buffer_alloc_just_right_returns_nonnull:0: Passed
tests/check_util.c:409:P:buffer:test_unaligned_buffer_alloc_returns_aligned:0: Passed
tests/check_util.c:423:P:buffer:test_buffer_alloc_returns_aligned:0: Passed
tests/check_util.c:429:E:buffer:test_null_buffer_zero_alloc_returns_nonnull:0: (after this point) Early exit with return value 1
tests/check_util.c:442:P:buffer:test_zero_buffer_zero_alloc_returns_nonnull:0: Passed
tests/check_util.c:452:P:buffer:test_nonzero_buffer_zero_alloc_returns_nonnull:0: Passed
tests/check_util.c:457:E:buffer:test_null_buffer_nonzero_alloc_returns_null:0: (after this point) Early exit with return value 1
tests/check_util.c:470:P:buffer:test_zero_buffer_nonzero_alloc_returns_null:0: Passed
tests/check_util.c:480:P:buffer:test_buffer_tiny_alloc_returns_nonnull:0: Passed
tests/check_util.c:490:P:buffer:test_tiny_buffer_tiny_alloc_returns_nonnull:0: Passed
tests/check_util.c:500:P:buffer:test_tiny_unaligned_buffer_tiny_alloc_returns_null:0: Passed
tests/check_util.c:511:P:buffer:test_tiny_buffer_second_alloc_returns_null:0: Passed
tests/check_util.c:521:P:buffer:test_tiny_buffer_one_too_big_alloc_returns_null:0: Passed
tests/check_util.c:535:P:buffer:test_buffer_alloc_returns_zeroed_memory:0: Passed
tests/check_util.c:594:P:userdata_to_addrtuple:test_userdata_to_addrtuple_returns_tuples:0: Passed
tests/check_util.c:683:P:userdata_to_addrtuple:test_userdata_to_addrtuple_buffer_too_small_returns_erange:0: Passed
tests/check_util.c:594:P:userdata_to_addrtuple:test_userdata_to_addrtuple_smallest_buffer_eventually_works:0: Passed
tests/check_util.c:594:P:userdata_to_addrtuple:test_userdata_to_addrtuple_nonnull_pat_is_used:0: Passed
tests/check_util.c:648:P:userdata_for_name_to_hostent:test_userdata_for_name_to_hostent_returns_hostent_4:0: Passed
tests/check_util.c:648:P:userdata_for_name_to_hostent:test_userdata_for_name_to_hostent_returns_hostent_6:0: Passed
tests/check_util.c:783:P:userdata_for_name_to_hostent:test_userdata_for_name_to_hostent_buffer_too_small_returns_erange:0: Passed
tests/check_util.c:648:P:userdata_for_name_to_hostent:test_userdata_for_name_to_hostent_smallest_buffer_eventually_works_4:0: Passed
tests/check_util.c:648:P:userdata_for_name_to_hostent:test_userdata_for_name_to_hostent_smallest_buffer_eventually_works_6:0: Passed
tests/check_util.c:648:P:name_and_addr_to_hostent:test_name_and_addr_to_hostent_returns_hostent_4:0: Passed
tests/check_util.c:648:P:name_and_addr_to_hostent:test_name_and_addr_to_hostent_returns_hostent_6:0: Passed
tests/check_util.c:897:P:name_and_addr_to_hostent:test_name_and_addr_to_hostent_buffer_too_small_returns_erange:0: Passed
tests/check_util.c:648:P:name_and_addr_to_hostent:test_name_and_addr_to_hostent_smallest_buffer_eventually_works_4:0: Passed
tests/check_util.c:648:P:name_and_addr_to_hostent:test_name_and_addr_to_hostent_smallest_buffer_eventually_works_6:0: Passed
FAIL check_util (exit status: 1)

+ exit 1