Add null guard for mControllers in MapLibreMapFragment dialog handler

[aaronbrethorst]

In MapLibreMapFragment.java, the negative button handler in createNoLocationDialog() iterates mapFragment.mControllers without a null check (line 1098):

for (MapModeController controller : mapFragment.mControllers) {

If the dialog is shown before setMapMode() initializes mControllers, this would NPE. In practice this is low risk since setMapMode() runs in initMap() before user-triggered dialogs, but a defensive null guard should be added for safety.

The same pattern exists in the Google flavor's BaseMapFragment — both should be fixed.

Fix:

if (mapFragment.mControllers != null) {
    for (MapModeController controller : mapFragment.mControllers) {
        controller.onLocation();
    }
}

Found during review of #1513.

[amanjn38]

@aaronbrethorst I will resolve this