wildmatch test: use a paranoia pattern from nul_match()

Use a pattern from the nul_match() function in t7008-grep-binary.sh to make sure that we don't just fall through to the "else" if there's an unknown parameter. This is something I added in commit 77f6f4406f ("grep: add a test helper function for less verbose -f \0 tests", 2017-05-20) to grep tests, which were modeled on these wildmatch tests, and I'm now porting back to the original wildmatch tests. I am not using the "say '...'; exit 1" pattern from t0000-basic.sh because if I fail I want to run the rest of the tests (unless under -i), and doing this makes sure we do that and don't exit right away without fully reporting our errors. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>