Pen tool: do not merge with ancestor layer as it breaks the graph

[0HyperCube]

Reproduction

• Create a path with pen tool
• Add a separate contour to the layer by using shift with the pen tool
• Put the single path layer into a group
• Select the original path layer
• Use the pen tool to connect up the two contours.
• Observe graph is broken as the pen tool attempts to merge the layer with itself and fails miserably leaving an uncommitted transaction and some broken state.

Reported by

Chambers on discord