Allow mech.__str__ to be dotted form

Validate that sasl_name is nonempty before assigning it to base;
this prevents the situation where the sasl_name query succeeds,
but the contents of the name are empty.

Signed-off-by: Alexander Scheel <alexander.m.scheel@gmail.com>

Author: cipherboy

gssapi/mechs.py

@@ -56,7 +56,7 @@ def __unicode__(self):
 
     def _bytes_desc(self):
         base = self.dotted_form
-        if rfc5801 is not None:
+        if rfc5801 is not None and self._saslname and self._saslname.mech_name:
             base = self._saslname.mech_name
 
         if isinstance(base, six.text_type):