Reworked reopening last tab to no longer use recursion

A reviewer of the pull request was concerned about recursion. I changed
the code to be iterative.

osu.Game/Online/Chat/ChannelManager.cs

@@ -445,32 +445,46 @@ namespace osu.Game.Online.Chat
                 return;
             }
 
+            // This nested loop could be eliminated if a check was added so that
+            // when the code opens a channel it removes from the closedChannel list.
+            // However, this would require adding an O(|closeChannels|) work operation 
+            // every time the user joins a channel, which would make joining a channel
+            // slower. I wanted to centralize all major slowdowns so they
+            // can only occur if the user actually decides to use this feature.
+            for (int i = closedChannels.Count - 1; i >= 0; i--)
+            {
                 string lastClosedChannelName = closedChannels.Last();
                 closedChannels.RemoveAt(closedChannels.Count - 1);
-
+                bool alreadyJoined = false;
-            // types did not work with existing enumerable interfaces funcitons like Contains
+                // If the user already joined the channel, do not
-            for (int i = 0; i < joinedChannels.Count; i++)
+                // try to join it
+                for (int j = 0; j < joinedChannels.Count; j++)
                 {
-                // If the user already joined the channel, try the next
+                    if (joinedChannels[j].Name == lastClosedChannelName)
-                // channel in the list
-                if (joinedChannels[i].Name == lastClosedChannelName)
                     {
-                    JoinLastClosedChannel();
+                        alreadyJoined = true;
-                    return;
+                        break;
                     }
                 }
 
+                if (alreadyJoined == false)
+                {
                     Channel lastClosedChannel = AvailableChannels.FirstOrDefault(c => c.Name == lastClosedChannelName);
 
                     if (lastClosedChannel == null)
                     {
-                JoinLastClosedChannel();
+                        continue;
                     }
                     else
                     {
                         JoinChannel(lastClosedChannel);
+                        return;
                     }
                 }
+            }
+        }
+
+
 
         private long lastMessageId;