t7510: exit for loop with test result

t7510 uses for loops in a subshell, which need to make sure that the test
returns with the appropriate error code from within the loop.

Restructure the loops as the usual && chains with a single point of
"exit 1" at the end of the loop to make this clearer.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: Michael J Gruber

t/t7510-signed-commit.sh

@@ -50,7 +50,7 @@ test_expect_success GPG 'show signatures' '
 		for commit in initial second merge fourth-signed fifth-signed sixth-signed master
 		do
 			git show --pretty=short --show-signature $commit >actual &&
-			grep "Good signature from" actual || exit 1
+			grep "Good signature from" actual &&
 			! grep "BAD signature from" actual || exit 1
 			echo $commit OK
 		done
@@ -59,7 +59,7 @@ test_expect_success GPG 'show signatures' '
 		for commit in merge^2 fourth-unsigned sixth-unsigned seventh-unsigned
 		do
 			git show --pretty=short --show-signature $commit >actual &&
-			grep "Good signature from" actual && exit 1
+			! grep "Good signature from" actual &&
 			! grep "BAD signature from" actual || exit 1
 			echo $commit OK
 		done