Validate urls like http://.com or http://..com

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11702
| License       | MIT

This PR fixes the regular expression to accept valid URLs. It does not allow to start a domain name with "-" or "."
It is still valid (the test suite includes the domain `a.pl` as valid). The first part would match `a.p` and the second part `l`. Anyway, I think it could be clearer if we change it to `([\pL\pN\pS])([\pL\pN\pS\.\-])*`