rev-parse --show-prefix: add in trailing newline

Print out a trailing newline when --show-prefix is run with cwd
at the top level of the tree which results in an empty prefix.
Behavior is now like --show-cdup.

Fixes an expected failure in t1501.

Signed-off-by: Ross Lagerwall <rosslagerwall@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rev-parse.c

@@ -634,6 +634,8 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 			if (!strcmp(arg, "--show-prefix")) {
 				if (prefix)
 					puts(prefix);
+				else
+					putchar('\n');
 				continue;
 			}
 			if (!strcmp(arg, "--show-cdup")) {

t/t1501-worktree.sh

@@ -68,7 +68,7 @@ test_expect_success 'inside work tree' '
 	)
 '
 
-test_expect_failure 'empty prefix is actually written out' '
+test_expect_success 'empty prefix is actually written out' '
 	echo >expected &&
 	(
 		cd work &&