Fix editor crash due to mismanaged selected points on layers

[seam0s-dev]

Fixes #2636

[seam0s-dev]

Actions to be affected when anchors/handles overlays is toggled:

• Nudging selected points with shift+[arrow key].
• Reposition a selected point (primary handle, end handle or anchor) with mouse pointer.
• Move multiple selected points (primary handle, end handle or anchor) with mouse pointer.
• Selecting/deselecting points on the currently selected layer with the path tool.

Actions not to be affected when anchors/handles overlays is toggled:

• Changing selected filled layer(s) while in the path tool.
• Move around selected filled layer(s) while in the path tool. (currently, broken)

[Keavon]

Hi @seam0s-dev, thanks again for this code contribution to the project! We're still hoping you will respond to the request to relicense this code. Please see #4208 ASAP, thank you!