This is caused by a bug in Google drive where, in some circumstances
querying for "(A in parents) or (B in parents)" returns nothing
whereas querying for "A in parents" and "B in parents" separately
works fine.
This has been reported here:
https://issuetracker.google.com/issues/149522397
This workaround detects this condition by seeing if a listing for more
than one directory at once returns nothing.
If it does then it retries each one individually.
This can potentially have a false positive if the user has multiple
empty directories which are queried at once. The consequence of this
will be that ListR is disabled for a while until the directories are
found to be actually empty in which case it will be re-enabled.
Fixes#3114 and Fixes#4289
cbf3d43561