fix(polls): Returns an error on duplicate poll.

resources/prosody-plugins/mod_polls.lua

@@ -115,7 +115,8 @@ module:hook("message/bare", function(event)
 
         if room.polls.by_id[data.pollId] ~= nil then
             module:log("error", "Poll already exists: %s", data.pollId);
-            return;
+            event.origin.send(st.error_reply(event.stanza, 'cancel', 'not-allowed', 'Poll already exists'));
+            return true;
         end
 
         local answers = {}