[CHANGE] Client handling

Manager.YouTube/YouTubeClientCollection.cs

@@ -8,4 +8,17 @@ public class YouTubeClientCollection : KeyedCollection<string, YouTubeClient>
     {
         return item.Id;
     }
+
+    public new void Add(YouTubeClient client)
+    {
+        if (Items.Contains(client))
+        {
+            var index = Items.IndexOf(client);
+            Items[index] = client;
+        }
+        else
+        {
+            Items.Add(client);
+        }
+    }
 }