[fix] Avoid crash when the transform is not valid

LV crashes when we use Save/Load Paraview state with a lidar transform changed. A proxyProperty (transform) of a proxyPoperty (Interpreter) of a proxy (Reader or Stream) seems not handle by the paraview state. So the transform of an interpreter of a Reader/stream is null when it's loaded with the Paraview state.

This commit prevents LV to crash.

should be merge after lidarview-core!249 (merged)