Can't select points zero-length paths with rounded caps

Migrated from: https://bugs.launchpad.net/inkscape/+bug/985482

Steps to reproduce:

• open Inkscape
• open points.svg
• try to select the point by clicking on it
• try to move the point with the mouse

What happened?

Neither of the two operations are working.

What should have happened?

I can click-select and move the path by click-dragging.

Note: Square caps are not rendered (#1677 (moved)) so I can't test whether they are affected.

Inkscape Version and Operating System:

• Inkscape Version: 1.1-dev (c990a67, 2020-04-09)
• Operating System: Windows 10
• Operating System version: 10.0.18362

Migration info

There were a lot of tangentially related issues in the report, such as incorrect bounding box and bad Stroke-to-Path conversion. They have all been fixed.

Replicated since at least 0.48.3.1.