The SQL thread and a user connection executing SHOW SLAVE STATUS
have a race condition on Last_SQL_Errno, such that a slave which
previously errored and stopped, on its next start, SHOW SLAVE STATUS
can show that the SQL Thread is running while the previous error is
also showing.

The fix is to move when the last error is cleared when the SQL
thread starts to occur before setting the status of
Slave_SQL_Running.

Thanks to Kristian Nielson for his work diagnosing the problem!

Reviewed By:
============
Andrei Elkin <andrei.elkin@mariadb.com>
Kristian Nielson <knielsen@knielsen-hq.org>