Problem:
========
When attempting to delay a Slave attached with GTID, there appears to be an
extra delay applied initially. For example, this output reflects a Slave that is
already delayed by 43200 seconds. When switching to GTID replication,
replication is paused until SQL_Remaining_Delay counts down to 0:

CHANGE MASTER TO master_use_gtid=current_pos; CHANGE MASTER TO
MASTER_DELAY=43200;

Seconds_Behind_Master: 44847
Using_Gtid: Current_Pos
SQL_Delay: 43200
SQL_Remaining_Delay: 43089
Slave_SQL_Running_State: Waiting until MASTER_DELAY seconds after master
executed event

Analysis:
=========
When slave initiates a GTID based connection request to master, the master sends
two GTID_LIST events.  The first one is actual GTID_LIST event and the second
one is a fake GTID_LIST event. This is sent by master to provide its current
binlary log file position. The fake GTID_LIST events will have their ev->when=0.
'when' (the timestamp) is set to 0 so that slave could distinguish between real
and fake Rotate events.

On slave side when MASTER_DELAY is configured to "X" the applier will ensure
that there is a time delay of "X" seconds before the event is applied.

General behaviour of MASTER_DELAY example:-

Master
timestamp of event e1=10
timestamp of event e2=11

On slave MASTER_DELAY=5
Event e1 will be applied at = 15
e2 will be applied at =16

In bug scenario:-

On Master: With GTIDs
timestamp of event e1=10
timestamp of event e2=0

On Slave:
e1 will be applied at = 10 + 5 =15
For e2, since "e2->when=0" e2->when is set to current timestamp.
i.e since the e2->when and current timestamp on slave is the same applier waits
for additional master_delay=5 seconds. the ev->when contributes to
"rli->last_master_timestamp".

rli->last_master_timestamp= ev->when + (time_t) ev->exec_time;

Fake events should not update the "ev->when" to "current timestamp" on slave.

Fix:
===
Remove the assignment of current timestamp to "ev->when" when "ev->when=0".