Disposing Controls twice freezes BlishHud

[Robin Hentschel]

Adding a Control type like a button to a view multiple times crashes BlishHud when the View is being disposed of.

1. Add a Control Type to a View twice (in my case, a button to a settings view)
2. Set the buttons parent via the parent field
3. add the button via .AddChild(button) again
4. Observe BlishHud Freezing upon Disabling the Module

This is definitely a user error, but I would expect adding a control twice to be caught beforehand or an exception is thrown when the element is to be disposed of again.