t4205: don't exit test script on failure

Only abort the individual check instead of exiting the whole test script
if git show fails.  Noticed with GIT_TEST_PASSING_SANITIZE_LEAK=check.

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4205-log-pretty-formats.sh

@@ -156,7 +156,7 @@ test_expect_success 'NUL termination with --reflog --pretty=oneline' '
 	for r in $revs
 	do
 		git show -s --pretty=oneline "$r" >raw &&
-		cat raw | lf_to_nul || exit 1
+		cat raw | lf_to_nul || return 1
 	done >expect &&
 	# the trailing NUL is already produced so we do not need to
 	# output another one