Previous commit e7ca5b25cb combined
checks for filtered folders in one place. However, it turns out there
was a reason to have them separate. getfolder() on a non-existent Maildir
fails and there might not be an equivalent local Maildir folder for a
filtered out IMAP folder.
Fix this by first checking if the remote folder should be filtered, and
only then retrieving the local folder (which should exist then).
This bug was found by our test suite!
Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>