Emptied-out costumes retain their previous rotation centers

[adroitwhiz]

Expected Behavior

The rotation center of an empty costume should be (0, 0).

Actual Behavior

When the contents of a costume are deleted in the paint editor, the now-empty costume's rotation center will still be set to whatever it was previously, only being set to (0, 0) upon a reload. This can cause fencing issues.

See here for an instance of this.

Steps to Reproduce

1. Open the paint editor
2. Delete the contents of the current costume
3. Observe how far the sprite is now fenced from the edges

Operating System and Browser

N/A

[fsih]

While investigating this issue we found 2 related but different issues (running on a build with your fix patched)

The rotation center of a costume with width 0 but height non-zero should maybe not be 0,0

When switching to a costume with width 0, the rotation center doesn't appear to get updated