cdr.c: Set event time on party b when leaving a parking bridge

When Alice calls Bob and Bob does a blind transfer to Charlie,
Bob's bridge leave event generates a finalize on both the party_a
and party_b CDRs but while the party_a CDR has the correct end time
set from the event time, party_b's leg did not. This caused that
CDR's end time to be equal to the answered time and resulted in a
billsec of 0.

* We now pass the bridge leave message event time to
cdr_object_party_b_left_bridge_cb() and set it on that CDR before
calling cdr_object_finalize() on it.

NOTE:  This issue affected transfers using chan_sip most of the
time but also occasionally affected chan_pjsip probably due to
message timing.

ASTERISK-28677
Reported by: Maciej Michno

Change-Id: I790720f1e7326f9b8ce8293028743b0ef0fb2cca