When YOURLS replies with statusCode 200 but no "shorturl" field,
YourlsProxy::_extractShortUrl() returned int 0 for its ?string return
type. Under the file's declare(strict_types=1) this raises an uncaught
TypeError, aborting paste creation instead of surfacing the intended
"Error parsing proxy response" message. Fall back to null (matching
ShlinkProxy) so the existing graceful error path is taken.
Co-Authored-By: Claude <noreply@anthropic.com>
This should definitively rule out any circumstances, where invalid URLs could cause problems.
Both URL validity is checked before it is forwarded to the URL shortener proxy _and_ the host part is explicitly compared to make sure the domain is really the same one.
TOOD:
* [ ] some tests may be needed here (hmpff…)
