t7003-filter-branch: Fix test of a failing --msg-filter.

The test passed for the wrong reason: If the script given to --msg-filter
fails, it is expected that git-filter-branch aborts. But the test forgot
to tell the branch name to rewrite, and so git-filter-branch failed due to
incorrect usage.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7003-filter-branch.sh

@@ -114,7 +114,7 @@ test_expect_success 'use index-filter to move into a subdirectory' '
 
 test_expect_success 'stops when msg filter fails' '
 	old=$(git rev-parse HEAD) &&
-	! git-filter-branch -f --msg-filter false &&
+	! git-filter-branch -f --msg-filter false HEAD &&
 	test $old = $(git rev-parse HEAD) &&
 	rm -rf .git-rewrite
 '