Refactor server_start() error handling

This avoids cleanup duplication.

app/src/server.c

@@ -345,32 +345,33 @@ server_start(struct server *server, const char *serial,
     }
 
     if (!push_server(serial)) {
-        SDL_free(server->serial);
+        goto error1;
-        return false;
     }
 
     if (!enable_tunnel_any_port(server, params->port_range)) {
-        SDL_free(server->serial);
+        goto error1;
-        return false;
     }
 
     // server will connect to our server socket
     server->process = execute_server(server, params);
-
     if (server->process == PROCESS_NONE) {
+        goto error2;
+    }
+
+    server->tunnel_enabled = true;
+
+    return true;
+
+error2:
     if (!server->tunnel_forward) {
         close_socket(&server->server_socket);
     }
     disable_tunnel(server);
+error1:
     SDL_free(server->serial);
     return false;
 }
 
-    server->tunnel_enabled = true;
-
-    return true;
-}
-
 bool
 server_connect_to(struct server *server) {
     if (!server->tunnel_forward) {