Fix exception when changing an external tilemap file after it was initially missing

[4ian]

• Fix not removeChild being done so an extra pixi object was staying in the PIXI container of instances - leading to containsPoint being called on something that was supposed to have disappeared (and crashing because sprite transform in PIXI was gone).
• Also add a proper error message and bug report in case of crash in PIXI rendering (but this would not be triggered by the problem fixed here - this is a different kind of exception being reported).
• Asked on PixiJS github if we can catch exceptions in the "event handling"/interaction manager of PixiJS: try/catch for EventBoundary/EventSystem pixijs/pixijs#10910

[D8H]

LGTM