transport-helper: fix strbuf leak in push_refs_with_push()

We loop over the refs to push, building up a strbuf with the set of
"push" directives to send to the remote helper. But if the atomic-push
flag is set and we hit a rejected ref, we'll bail from the function
early. We clean up most things, but forgot to release the strbuf.

Fixing this lets us mark t5541 as leak-free.

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

Author: peff

t/t5541-http-push-smart.sh

@@ -7,6 +7,7 @@ test_description='test smart pushing over http via http-backend'
 GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 ROOT_PATH="$PWD"

transport-helper.c

@@ -1023,6 +1023,7 @@ static int push_refs_with_push(struct transport *transport,
 			if (atomic) {
 				reject_atomic_push(remote_refs, mirror);
 				string_list_clear(&cas_options, 0);
+				strbuf_release(&buf);
 				return 0;
 			} else
 				continue;