Little things

See #1344 for more details.

I've added a commit to fix a few warnings.
I decided not to do what I said [here](https://github.com/skurfer/Quicksilver/commit/0f7ab136145e95e1ff04409b73a4303bf632f510#commitcomment-2480120) since we only ever reach this method if the `urlString` is recognised as a URL, and at the moment that means if it has the `mailto:` prefix *or* a scheme.