Fix another collision shape editor crash

[KoBeWi]

The collision shape editor checks in NOTIFICATION_PROCESS if the shape has not changed. In theory it should ensure that the shape is valid before trying to draw it. But turns out, for whatever reason, and contrary to the "Clear" context menu option, the revert arrow will remove the shape somewhere between NOTIFICATION_PROCESS and drawing function, which results in redraw with old data.

The PR makes the draw method use the currently cached shape, which means that in the aforementioned corner-case, the editor will draw old shape for a single frame.
Of course an alternative is adding a null check for node's shape, but the current_shape is updated reliably, so why not use it.

Fixes #76771

[Rindbee]

The main reason for #76771 is that shape is reset to null, but shape_type is not reset to -1. The data in CollisionShape2DEditor has not been updated yet.

CollisionShape2D does not emit a signal when its shape is reset to another shape. This caused CollisionShape2DEditor to fail to update the data in time.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 4.0.3.