Fix: Surface Colour/Transparency KeyError Crash - #1377

  def SetActorTransparency(self, surface_index, transparency):
+     if surface_index not in self.actors_dict:
+         return
      self.actors_dict[surface_index].GetProperty().SetOpacity(1 - transparency)

  def SetActorColour(self, surface_index, colour):
+     if surface_index not in self.actors_dict:
+         return
      self.actors_dict[surface_index].GetProperty().SetColor(colour[:3])