Destroy the preview sprite if we are moving on

SpriteLibrary/SpriteEntryForm.cs

@@ -475,6 +475,7 @@ namespace SpriteLibrary
                 DialogResult Answer = MessageBox.Show("You have unsaved Changes.  Would you like to save them before proceeding?","Save?",MessageBoxButtons.YesNoCancel);
                 if (Answer == DialogResult.Yes) ApplyChanges();
                 if (Answer == DialogResult.Cancel) return false;
+                if (PreviewSprite != null) PreviewSprite.Destroy();
             }
             return true;
         }