[Builtins] Fix for ReloadSkin() while dialogs are opened.

If you reload the skin while the context menu is open for example, then that dialog won´t work anymore until you restart Kodi.
This almost exclusively happens for skinners while debugging, but could also be triggered in real-world cases. (some skins and add-ons use that builtin for different stuff)
This PR force-closes all dialogs before reloading / unloading the skin.