Send IQ response for gamereport requests

XMPP demands a response for every IQ get/set stanza. This wasn't the
case for gamereport requests yet, so this commit adds it.

While Pyrogenesis neither expects nor handles these responses, it
doesn't result in any problems either.

xpartamupp/echelon.py

@@ -678,10 +678,15 @@ def _iq_game_report_handler(self, iq):
         if not iq['from'].resource.startswith('0ad'):
             return
 
+        iq_r = iq.reply()
+
         try:
             self.report_manager.add_report(iq['from'], iq['gamereport']['game'])
         except Exception:
             logger.exception("Failed to update game statistics for %s", iq['from'].bare)
+            iq_r["error"]["condition"] = "internal-server-error"
+
+        iq_r.send()
 
         rating_messages = self.leaderboard.get_rating_messages()
         if rating_messages: