Pass message containing remaining directories to check. Account widget
will recursively call CheckMail with the remaining directories until
a Done message is returned.
Only needed for IMAP worker as other workers run check-mail-cmd in
a separate goroutine.
Suggested-By: Tim Culverhouse <tim@timculverhouse.com>
Signed-off-by: kt programs <ktprograms@gmail.com>
Tested-by: Tim Culverhouse <tim@timculverhouse.com>