Segfault in poincare when no variables

[d-torrance]

The builds in #4099 uncovered the following bug:

i1 : R = QQ[]

o1 = R

o1 : PolynomialRing

i2 : poincare ideal 1_R
-- SIGSEGV
-* stack trace, pid: 212314
 0# profiler_stacktrace(std::ostream&, int) at /usr/src/macaulay2-1.25.11+git202601190345-0ppa202601191512~ubuntu24.04.1/M2/Macaulay2/d/main.cpp:131
 1# segv_handler at /usr/src/macaulay2-1.25.11+git202601190345-0ppa202601191512~ubuntu24.04.1/M2/Macaulay2/d/main.cpp:243
 2# 0x0000763FC0845330 in /usr/lib/x86_64-linux-gnu/libc.so.6
 3# partition_table::partition(MonomialIdeal*&, std::vector<MonomialIdeal*, gc_allocator<MonomialIdeal*> >&) at /usr/src/macaulay2-1.25.11+git202601190345-0ppa202601191512~ubuntu24.04.1/M2/Macaulay2/e/hilb.cpp:126
 4# hilb_comp::next_monideal() at /usr/src/macaulay2-1.25.11+git202601190345-0ppa202601191512~ubuntu24.04.1/M2/Macaulay2/e/hilb.cpp:322
 5# hilb_comp::hilb_comp(PolynomialRing const*, Matrix const*) at /usr/src/macaulay2-1.25.11+git202601190345-0ppa202601191512~ubuntu24.04.1/M2/Macaulay2/e/hilb.cpp:369
 6# hilb_comp::hilbertNumerator(Matrix const*) at /usr/src/macaulay2-1.25.11+git202601190345-0ppa202601191512~ubuntu24.04.1/M2/Macaulay2/e/hilb.cpp:674
 7# IM2_Matrix_Hilbert at interface/groebner.cpp:72
 8# interface_rawHilbert at /usr/src/macaulay2-1.25.11+git202601190345-0ppa202601191512~ubuntu24.04.1/M2/Macaulay2/d/interface.dd:2615

Cc: @mikestillman