stash: add a test for stash create with no files

Ensure the command suceeds and outputs nothing

Signed-off-by: Joel Teichroeb <joel@teichroeb.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3903-stash.sh

@@ -444,6 +444,14 @@ test_expect_failure 'stash file to directory' '
 	test foo = "$(cat file/file)"
 '
 
+test_expect_success 'stash create - no changes' '
+	git stash clear &&
+	test_when_finished "git reset --hard HEAD" &&
+	git reset --hard &&
+	git stash create >actual &&
+	test_must_be_empty actual
+'
+
 test_expect_success 'stash branch - no stashes on stack, stash-like argument' '
 	git stash clear &&
 	test_when_finished "git reset --hard HEAD" &&