`tel:` links not working with plus sign

Internationally formatted phone numbers starting with the plus sign are not currently being recognized as valid links, and they end up being stripped out. That’s true whether we use tel:+1234 (the correct form) or tel://+1234 (the form accepted by Discourse, and that seems to work in browsers too). Also tested with %2B just in case, but that doesn’t work either. The only thing that seems to work is tel://1234.

Here is an example, that likely won’t work in both cases because tel needs to be enabled in the configuration:

That was tested in 1.9.0.beta16.