WinGui: Remove another exception for queue handling and just handle t…

…he condition appropriately HandBrake#211

win/CS/HandBrakeWPF/Services/Queue/QueueProcessor.cs

@@ -505,7 +505,7 @@ public void Start(bool isClearCompleted)
         {
             if (this.IsProcessing)
             {
-                throw new Exception("Already Processing the Queue");
+                return;
             }
 
             this.clearCompleted = isClearCompleted;