Fix errors with invalid CollisionPolygon2D
Fix errors with invalid CollisionPolygon2D

Fixed internal errors when the shape is invalid and made warnings more
descriptive.

(cherry picked from commit 2217e477b98817595beb7316e6bea9c2d5c6221a)

ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot