For partial imports of mass exports, don't create empty locations for skipped sightings

[Adam Winer]

When doing a bulk eBird MyData import, and a lot of sightings get skipped (with the “mass import” duplicate missing), skipped sightings might still produce new locations.

[scythebill]

Resolve Issue #554: For partial imports of mass exports, don't create empty locations for skipped sightings

This also fixes locations getting added for cancelled or otherwise failed imports. The ReportSet is still marked dirty, which isn't ideal, but this does seem much better.

→ <<cset 33f3d2b6eb15>>