t5516: introduce 'push ref expression with non-existent oid src'

It is possible to trigger a Git bug by pushing a refspec where the
source is an oid that's non-existent. An example of the error message
produced is as follows:

	error: The destination you provided is not a full refname (i.e.,
	starting with "refs/"). We tried to guess what you meant by:

	- Looking for a ref that matches 'branch' on the remote side.
	- Checking if the <src> being pushed ('0000000000000000000000000000000000000001')
	  is a ref in "refs/{heads,tags}/". If so we add a corresponding
	  refs/{heads,tags}/ prefix on the remote side.

	Neither worked, so we gave up. You must fully qualify the ref.
	BUG: remote.c:1221: '0000000000000000000000000000000000000001' should be commit/tag/tree/blob, is '-1'
	fatal: the remote end hung up unexpectedly
	Aborted (core dumped)

Document this failure in a test case so that it can be confirmed fixed
later.

Signed-off-by: Denton Liu <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: Denton-L

t/t5516-fetch-push.sh

@@ -509,6 +509,13 @@ test_expect_success 'push ref expression with non-existent, incomplete dest' '
 
 '
 
+test_expect_failure 'push ref expression with non-existent oid src' '
+
+	mk_test testrepo &&
+	test_must_fail git push testrepo $(test_oid 001):branch
+
+'
+
 for head in HEAD @
 do