Eraser tool: Clip mode crashes on clones

Separated from #2622 (closed)

Steps to reproduce:

• create a rectangle
• clone it
• activate Eraser tool, Mode: "Clip"
• move the eraser in one stroke over clone and original
• repeat the last step

What happened?

Crash. Backtrace by @nathanal: inkscape-backtrace-eraser-clipping-clone.txt

What should have happened?

No crash.

Inkscape Version and Operating System:

• Inkscape Version: 1.0 (5b275a35d9, 200-0503) snap
• Operating System: Ubuntu
• Operating System version: 20.04