nav: use mapChanged signal alongside isFullyLoaded()

selfdrive/ui/qt/maps/map.cc

@@ -241,6 +241,11 @@ void MapWindow::initializeGL() {
   m_map->setStyleUrl("mapbox://styles/commadotai/ckq7zp8ts1k0o17p8m6rv6cet");
 
   connect(m_map.data(), SIGNAL(needsRendering()), this, SLOT(update()));
+  QObject::connect(m_map.data(), &QMapboxGL::mapChanged, [=](QMapboxGL::MapChange change) {
+    if (change == QMapboxGL::MapChange::MapChangeDidFinishLoadingMap) {
+      loaded_once = true;
+    }
+  });
   timer->start(100);
 }