fix for volunteer added but no emails goes out to opportunity owners error

Emails were not being generated by system when someone volunteered for a opportunity due to two errors. 
1) Volunteer ID was not set / being passed as the code expected it to be so it was empty when it was attempted to be used
2) The check to prevent sending emails to yourself when you take an action was always succeeding because the initiator was always the same as the task owner in the case of a volunteer volunteering.
And it should be `|| null` not `0`