title: Android setting custom icon to marker returns null in Marshmallow
body: <p>I'm trying to set custom icons for markers in google maps, it works fine with my phone that runs android 4.1.2, but I then tested my app with a Samsung Galaxy tabS2 that runs 6.0.1 and it seems that it can't find the icons.
  Below there is my code</p>
  
  <pre><code>@Override
  public void onMapReady(GoogleMap googleMap) {
      deviceMap = googleMap;
      deviceMap.setOnMapClickListener(new GoogleMap.OnMapClickListener() {
          @Override
          public void onMapClick(LatLng point) {
              if(customM != null)
                  customM.remove();
              customM = deviceMap.addMarker(new MarkerOptions().position(point).icon(bmD).title(getString(R.string.customPos)));
          }
      });
      if (deviceMap != null) {
          try{
              Bitmap bm = BitmapFactory.decodeResource(getResources(), R.drawable.temp_bts_icon);
              deviceM = deviceMap.addMarker(new MarkerOptions().position(devicePos).title(getString(R.string.devicePos))
                      .icon(BitmapDescriptorFactory.fromBitmap(bm)));
              bm = BitmapFactory.decodeResource(getResources(), R.drawable.phone);
              telephoneM = deviceMap.addMarker(new MarkerOptions().position(telephonePos).title(getString(R.string.telephonePos))
                      .icon(BitmapDescriptorFactory.fromBitmap(bm)));
          }catch (Exception e){
              Toast.makeText(Globals.MainActivity, "Error retrieving icons", Toast.LENGTH_SHORT).show();
              deviceM = deviceMap.addMarker(new MarkerOptions().position(devicePos).title(getString(R.string.devicePos))
                      .icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_AZURE)));
              telephoneM = deviceMap.addMarker(new MarkerOptions().position(telephonePos).title(getString(R.string.telephonePos))
                      .icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_ORANGE)));
          }
  
          updateDeviceMarker();
          deviceMap.getUiSettings().setMyLocationButtonEnabled(true);
          deviceMap.getUiSettings().setZoomGesturesEnabled(true);
          deviceMap.getUiSettings().setZoomControlsEnabled(true);
          deviceMap.getUiSettings().setCompassEnabled(true);
          deviceMap.getUiSettings().setAllGesturesEnabled(true);
          deviceMap.moveCamera(CameraUpdateFactory.newLatLngZoom(deviceM.getPosition(), 1f));
      }
  }
  </code></pre>
  
  <p>I also tried doing this:</p>
  
  <pre><code> telephoneM = deviceMap.addMarker(new MarkerOptions().position(telephonePos).title(getString(R.string.telephonePos).icon(BitmapDescriptorFactory.fromResource(R.drawable.temp_bts_icon));
  </code></pre>