Fix PhabricatorBot ignore messages from senders
Summary:
PhabricatorBotMessage->getSender returns a PhabricatorBotUser object (which potentially can be null)
So check null and then use getName to get actual name of the sender
Test Plan: Run phabot and add myself to ignore list
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, Korvin
Differential Revision: https://secure.phabricator.com/D5036