add error message for long URLs

Currently there's no error to let user know the URL isn't being broadcast if it is too long.
For testing, this works: `https://circuitpython.org/`
This doesn't: `https://circuitpython.org/libraries`

No file or test is named in the issue. Start by locating the code path that broadcasts the supplied URL and compare the working and failing examples, then identify how an overlong URL is handled. Done means the user receives an error when the URL cannot be broadcast because it is too long.

Written by the indexing model from the issue text.