message: Fix bug in PolarTileDataSource
  Tiles that are generated by the PolarTileDataSource without a material
  return early, they have no geometry, so the VisibleTileSet thinks
  that these are still loading, and the FRAME_COMPLETE event never arrives,
  by forcing the geometry, then we get the FRAME_COMPLETE event.
diff: @@ -205,6 +205,7 @@ export class PolarTileDataSource extends DataSource {
  const isNorthPole = north > 0 && south >= 0;
  const material = isNorthPole ? this.m_northPoleMaterial : this.m_southPoleMaterial;
  if (material === undefined) {
  + tile.forceHasGeometry(true);
  return;
  }
  