commit: release strbuf on error return in commit_tree_extended()

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

commit.c

@@ -1564,10 +1564,13 @@ int commit_tree_extended(const char *msg, size_t msg_len,
 	if (encoding_is_utf8 && !verify_utf8(&buffer))
 		fprintf(stderr, _(commit_utf8_warn));
 
-	if (sign_commit && do_sign_commit(&buffer, sign_commit))
-		return -1;
+	if (sign_commit && do_sign_commit(&buffer, sign_commit)) {
+		result = -1;
+		goto out;
+	}
 
 	result = write_sha1_file(buffer.buf, buffer.len, commit_type, ret);
+out:
 	strbuf_release(&buffer);
 	return result;
 }