Fix the uses of stanza.reply()

This is relying on the stanzas being copied for each handler. We no
longer do that for performance reasons, so instead of editing the copy
in-place, stanza.reply() now returns a new stanza.

slixmpp/plugins/xep_0009/rpc.py

@@ -93,7 +93,8 @@ class XEP_0009(BasePlugin):
 
     def _item_not_found(self, iq):
         payload = iq.get_payload()
-        iq.reply().error().set_payload(payload)
+        iq = iq.reply()
+        iq.error().set_payload(payload)
         iq['error']['code'] = '404'
         iq['error']['type'] = 'cancel'
         iq['error']['condition'] = 'item-not-found'
@@ -101,7 +102,8 @@ class XEP_0009(BasePlugin):
 
     def _undefined_condition(self, iq):
         payload = iq.get_payload()
-        iq.reply().error().set_payload(payload)
+        iq = iq.reply()
+        iq.error().set_payload(payload)
         iq['error']['code'] = '500'
         iq['error']['type'] = 'cancel'
         iq['error']['condition'] = 'undefined-condition'
@@ -109,7 +111,8 @@ class XEP_0009(BasePlugin):
 
     def _forbidden(self, iq):
         payload = iq.get_payload()
-        iq.reply().error().set_payload(payload)
+        iq = iq.reply()
+        iq.error().set_payload(payload)
         iq['error']['code'] = '403'
         iq['error']['type'] = 'auth'
         iq['error']['condition'] = 'forbidden'
@@ -117,7 +120,8 @@ class XEP_0009(BasePlugin):
 
     def _recipient_unvailable(self, iq):
         payload = iq.get_payload()
-        iq.reply().error().set_payload(payload)
+        iq = iq.reply()
+        error().set_payload(payload)
         iq['error']['code'] = '404'
         iq['error']['type'] = 'wait'
         iq['error']['condition'] = 'recipient-unavailable'