Research how godot handles csharp exceptions during _Ready calls

[Abb4]

When exceptions appear during _Ready calls, they seem to abort initialization but they don't flag node as invalid and don't crash the game.

• research what godot suggests for critical errors
• decide on how to handle critical errors during initialization (classic one is that a editor property is not set, see Replace editor-not-null-attribute assertions using NodeErrors with alternatives that don't use NodeErrors #90)