wildmatch test: use a paranoia pattern from nul_match()

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>