Catastrofic backtracking fix

[DemonTPx]

trafficstars

Fixes #425

Update setHostInContent regexes to reduce steps and hopefully prevent a PREG_BACKTRACK_LIMIT_ERROR and check result of preg_replace to be sure we do not set content or description to null.

Also refactor setHostInContent and getHostFromLink a bit for readability.

cc @IgorA100

[DemonTPx]

I also tested the updated regex again with a modified version of the feed item, see:

https://regex101.com/r/oxU67Z/1

[IgorA100]

I see this problem with your link. I'll think about a solution.