Issue #3622994: Uncaught MalformedUriException from Guzzle crashes cron when a link's URL is malformed

Issue #3622994 by bond708: Catch exceptions thrown while building the request so a malformed link URL cannot crash cron Fixes an uncaught GuzzleHttp\Psr7\Exception\MalformedUriException that crashes cron whenever a checked link's URL is malformed (e.g. an invalid host). LinkCheckerService::check() now catches any exception thrown while building the request and routes it through the existing exceptionHandling() path, so the link is recorded as broken (502) instead of taking down cron. ▎ ▎ Complements #3607990, which prevents whitespace-only malformed URLs but doesn't guard against other cases Guzzle can reject.

Closes #3622994