Merge branch 'ps/object-collision-check'

CI jobs gave sporadic failures, which turns out that that the
object finalization code was giving an error when it did not have
to.

* ps/object-collision-check:
  object-file: retry linking file into place when occluding file vanishes
  object-file: don't special-case missing source file in collision check
  object-file: rename variables in `check_collision()`
  object-file: fix race in object collision check

diff --cc object-file.c
Simple merge