gotr: fixed message injection without session

gotr/manifest.ini

 [info]
 name: Off-The-Record Encryption
 short_name: gotr
-version: 1.5
+version: 1.6
 description: See http://www.cypherpunks.ca/otr/
 authors: Kjell Braden <afflux.gajim@pentabarf.de>
 homepage: http://gajim-otr.pentabarf.de

gotr/otrmodule.py

@@ -97,11 +97,11 @@ class GajimContext(potr.context.Context):
         account = self.user.accountname
 
         stanza = common.xmpp.Message(to=self.peer, body=msg, typ='chat')
-        if appdata and 'session' in appdata:
-            session = appdata['session']
-            stanza.setThread(session.thread_id)
+        if appdata is not None:
+            session = appdata.get('session', None)
+            if session is not None:
+                stanza.setThread(session.thread_id)
         gajim.connections[account].connection.send(stanza, now=True)
-        return
 
     def setState(self, newstate):
         if self.state == potr.context.STATE_ENCRYPTED: