Skip Drag & Drop filtering for DNS-safe URLs (no hostname, e.g. RFC3966 tel:)
Some URLs are convenient to drag & drop (e.g. [phone numbers embedded in tel: URLs)](https://forum.torproject.net/t/drag-and-drop-protections-in-tor-browser-12-0/5854/10) and cannot trigger unwanted DNS requests because they've got no hostname. Let's avoid filtering them.
issue