fix double dispose from finalizer

Author: pandinocoder

Intersect.Client.Framework/Graphics/GameTexture.cs

@@ -418,6 +418,11 @@ private void EmitUnloaded()
 
     private void Dispose(bool disposing)
     {
+        if (!disposing && _disposed)
+        {
+            return;
+        }
+
         ObjectDisposedException.ThrowIf(_disposed, this);
 
         _disposed = true;