foobar2000.exe spotify:url doesn't open

Executing `foobar2000.exe spotify:track:2ZIfv0fO740IFZdTJTP1JA` gives:

```
Unable to open item for playback (Unsupported file format):
"C:\foobar2000\spotify:track:2ZIfv0fO740IFZdTJTP1JA"
```

...as foobar2000 helpfully attempts to resolve this to a path.

As anything with colons in is _bogglingly_ unlikely to be a real file, we should probably just strip anything before "spotify:" in a URL.
