repository/IMAP.py getselectors updated

In the patch "IMAP list folders" we updated the function getselectors
to return '""'. We use this variable in the folders, but also here.

Because the variable is never '', we need update it with this change, to
test that the variable has value, but is not empty.

Signed-off-by: Rodolfo García Peñas (kix) <kix@kix.es>

offlineimap/repository/IMAP.py

@@ -549,7 +549,7 @@ class IMAPRepository(BaseRepository):
         if foldername == '':
             return
 
-        if self.getreference():
+        if self.getreference() != '""':
             foldername = self.getreference() + self.getsep() + foldername
         if not foldername:  # Create top level folder as folder separator.
             foldername = self.getsep()