Modify path extensions will open closed paths

Migrated from: https://bugs.launchpad.net/inkscape/+bug/202540

Summary:

Closed paths get opened by applying "Modify Path" extensions.

Steps to reproduce:

• open Inkscape
• create a closed path
• go to "Extensions -> Modify Path -> Add Nodes…" and apply

What happened?

Nodes get added, plus an extra node AND the path is now open.

What should have happened?

Nodes get added, path remains closed.

Sample attachments:

path-close

Version Info:

- Inkscape Version: Inkscape 1.0 (4035a4fb49, 2020-05-01)
- Operating System: Manjaro
- Operating System version: rolling