Don't ask for username in the preauthtunnel case

repos.getuesr() asks for a username if none is specified, but in the
case of a tunnel connection, we don't need one, so we need to skip the
repos.getuser() call here.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

offlineimap/imapserver.py

@@ -56,7 +56,7 @@ class IMAPServer:
         self.config = repos.getconfig()
         self.tunnel = repos.getpreauthtunnel()
         self.usessl = repos.getssl()
-        self.username = repos.getuser()
+        self.username = None if self.tunnel else repos.getuser()
         self.password = None
         self.passworderror = None
         self.goodpassword = None