Disable certificate verification if there is no certificate

imaplib2 always attempts to verify a certificate if a verification
callback function is passed in, even the certificate is None
specified. Disable the verification excplictly by setting the
verification function to None in that case.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/imapserver.py

@@ -67,6 +67,8 @@ class IMAPServer:
         self.sslclientcert = repos.getsslclientcert()
         self.sslclientkey = repos.getsslclientkey()
         self.sslcacertfile = repos.getsslcacertfile()
+        if self.sslcacertfile is None:
+            self.verifycert = None # disable cert verification
         self.delim = None
         self.root = None
         self.maxconnections = repos.getmaxconnections()