Skips creating duplicate poltergeists for the same user. (#1925)

resources/prosody-plugins/mod_muc_poltergeist.lua

@@ -393,13 +393,19 @@ function handle_create_poltergeist (event)
         return 404;
     end
 
-    local username = generate_uuid();
-    store_username(room, user_id, username)
-
-    create_poltergeist_occupant(
-        room, string.sub(username,0,8), name, avatar, status);
-
-    return 200;
+    local username = get_username(room, user_id);
+    if (username ~= nil
+        and have_poltergeist_occupant(room, string.sub(username, 0, 8))) then
+        log("warn", "poltergeist for username:%s already in the room:%s",
+            username, room_name);
+        return 202;
+    else
+        username = generate_uuid();
+        store_username(room, user_id, username);
+        create_poltergeist_occupant(
+            room, string.sub(username, 0, 8), name, avatar, status);
+        return 200;
+    end
 end
 
 --- Handles request for updating poltergeists status