t0060: verify that real_path() fails if passed the empty string

It doesn't, so mark the test as failing.
Signed-off-by: NMichael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t0060-path-utils.sh

@@ -144,6 +144,10 @@ test_expect_success 'absolute path rejects the empty string' '
 	test_must_fail test-path-utils absolute_path ""
 '
 
+test_expect_failure 'real path rejects the empty string' '
+	test_must_fail test-path-utils real_path ""
+'
+
 test_expect_success SYMLINKS 'real path works as expected' '
 	mkdir first &&
 	ln -s ../.git first/.git &&