Fixed fatal when using fake load balancers.

The error was:
Catchable fatal error: Argument 1 passed to DatabaseMysql::masterPosWait()
must implement interface DBMasterPos, boolean given, called in
/var/www/DevWiki/core/includes/db/LoadBalancer.php on line 419

Change-Id: I230585930c1424b0868f9aa290167c66bc6848bd
Merge "Fixed fatal when using fake load balancers."