Fixes missing lookup var in ticket lock renews

Was receiving stack traces "Missing argument 2 for TicketLock::lookup()"
Which, according to Ticket::lookup should be $id,$tid.. 

The change works for 1.7 as well.

Modified a few other checks, as we can't exactly check for a 0 default value with a boolean.. but we do need the TicketID to find the correct lock.

This extends from https://github.com/osTicket/osTicket-1.8/pull/335 

Guess I didn't notice the functionality was missing as it might not have worked for a while.