check if connection is active before sending something.

src/adhoc_commands.py

@@ -487,7 +487,7 @@ class CommandWindow:
 	def send_cancel(self):
 		'''Send the command with action='cancel'. '''
 		assert self.commandnode is not None
-		if self.sessionid is not None:
+		if self.sessionid is not None and self.account.connection:
 			# we already have sessionid, so the service sent at least one reply.
 			stanza = xmpp.Iq(typ='set', to=self.jid)
 			stanza.addChild('command', attrs={