fix: EnvironmentSensorManager.cpp: don't update location if GPS is turned off.

previously the location would always snap to the last heard GPS location after GPS had been on.

src/helpers/sensors/EnvironmentSensorManager.cpp

@@ -220,7 +220,7 @@ void EnvironmentSensorManager::loop() {
   _location->loop();
 
   if (millis() > next_gps_update) {
-    if (_location->isValid()) {
+    if (gps_active && _location->isValid()) {
       node_lat = ((double)_location->getLatitude())/1000000.;
       node_lon = ((double)_location->getLongitude())/1000000.;
       MESH_DEBUG_PRINTLN("lat %f lon %f", node_lat, node_lon);