PSD fails to import r/o invites but leaves a stale folder

[adrianmay]

Independently of whether the linux or windows versions are used, when we generate a r/o invite from one instance and import it into another, the recipient fails the import but creates a local import directory by the requested name which appears on the UI as always syncing and blocks imports of any other folder to the same local directory name.

[hacklschorsch]

Moved to gridsync/gridsync#718.

[adrianmay]

Closing cos the ticket was moved.