close jingle audio/video request window when we click ok/cancel button is

seesion has been canceled. Fixes #7119

src/dialogs.py

@@ -5159,6 +5159,7 @@ class VoIPCallReceivedDialog(object):
         session = gajim.connections[self.account].get_jingle_session(self.fjid,
             self.sid)
         if not session:
+            dialog.destroy()
             return
         if response == gtk.RESPONSE_YES:
             #TODO: Ensure that ctrl.contact.resource == resource