Move & Organize defaults to the library's first path, not the file's own

[W-Floyd]

Superseded by #2406, which reproduces this on a clean Stable container, adds screenshots, and covers a second related defect (Current Path is also built from the library's first path, so the dialog misreports where the file currently is).

Opened here first because I had only verified it by reading the source. That is no longer true, so the issue is the accurate record — please refer to it rather than this thread. I would delete this, but deletion needs repo permissions I do not have.