t7501: add test of "commit --dry-run --short"

Add test for commit with --dry-run --short for a new file of zero
length.

The test demonstrates that the setting of the committable flag is
broken.

Signed-off-by: Stephen P. Smith <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: Stephen P. Smith

t/t7501-commit.sh

@@ -682,4 +682,10 @@ test_expect_success '--dry-run with conflicts fixed from a merge' '
 	git commit -m "conflicts fixed from merge."
 '
 
+test_expect_failure '--dry-run --short' '
+	>test-file &&
+	git add test-file &&
+	git commit --dry-run --short
+'
+
 test_done