Update phishing and pluralkit extension to use nullable functions and…

[NoComment1105]

… catch some more exceptions.

Previously, the phishing extension would relentlessly send exceptions for being unable to read URLs for various reasons, this is extremely frustrating since it's out of the users control. I've switch this to catch all exceptions, and log them at warn level instead, so they're still visible.

The PluralKit extension attempts to get channels using asChannelOf currently, resulting in class cast exceptions and null pointer exceptions. I have moves over to using asChannelOfOrNull to avoid the NPEs and surrounded initial attempts at using this function with a try/catch for ClassCastExceptions

[gdude2002]

This is more or less good - thanks for the contribution!