symbolic-ref: propagate error code from create_symref()

If create_symref() fails, git-symbolic-ref will still exit
with code 0, and our caller has no idea that the command did
nothing.

This appears to have been broken since the beginning of time
(e.g., it is not a regression where create_symref() stopped
calling die() or something similar).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/symbolic-ref.c

diff --git a/builtin/symbolic-ref.c b/builtin/symbolic-ref.c
index ce0fde7..9c29a64 100644
--- a/builtin/symbolic-ref.c
+++ b/builtin/symbolic-ref.c
@@ -67,7 +67,7 @@
 		if (!strcmp(argv[0], "HEAD") &&
 		    !starts_with(argv[1], "refs/"))
 			die("Refusing to point HEAD outside of refs/");
-		create_symref(argv[0], argv[1], msg);
+		ret = !!create_symref(argv[0], argv[1], msg);
 		break;
 	default:
 		usage_with_options(git_symbolic_ref_usage, options);

t/t1401-symbolic-ref.sh

diff --git a/t/t1401-symbolic-ref.sh b/t/t1401-symbolic-ref.sh
index 36378b0..e9219a9 100755
--- a/t/t1401-symbolic-ref.sh
+++ b/t/t1401-symbolic-ref.sh
@@ -63,4 +63,10 @@
 '
 reset_to_sane
 
+test_expect_success 'symbolic-ref reports failure in exit code' '
+	test_when_finished "rm -f .git/HEAD.lock" &&
+	>.git/HEAD.lock &&
+	test_must_fail git symbolic-ref HEAD refs/heads/whatever
+'
+
 test_done