Crash applying Boolean operations (e.g. union) to shapes with certain LPEs applied (Corner LPE)

Reported by Gqpunk in chat.inkscape.org (private conversation)

Steps to reproduce:

• Open Inkscape
• Create a rectangle (or a path)
• Apply Corner LPE (or offset LPE)
• With the object selected, apply union

What happened?

• crash
• In Inkscape 1.1-dev (7dffdfe0, 2021-01-10), inkscape-asan-crash-bool-on-lpe.txt
• In Inkscape 1.1-alpha (ec367c61, 2021-02-07) inkscape-backtrace-crash-bool-on-lpe.txt

What should have happened?

• no crash, like what happens when the only LPE applied is BSpline (and presumably spiro since change was tested with these: #548 (closed))

Version Info:

• Inkscape 1.1-alpha (ec367c61, 2021-02-07) Linux Mint 20
• Inkscape 1.0.2 (e86c8708, 2021-01-15) Linux Mint 20
• not replicated Inkscape 1.0.1 (3bc2e813, 2020-09-07) Linux Mint 20
• Bisection points to 1921e68f (1.0.x) and 53d95db0 on trunk.