Reopening same project folder closes all open files

[peterflynn]

1. Put some files into the working set
2. Choose File > Open Folder
3. Choose the same folder that you already have open

Result: all open files are closed
(you'll get unsaved changes confirmation if applicable, though -- so no data loss)

Expected: all files remain open, just as if you'd switched from a different project to this one (ideally, it should be a total no-op)

[njx]

Reviewed. Low priority, leaving unassigned since we have a community pull request for it.

[RaymondLim]

Fix confirmed.