Minimal fix for Wikibase related SpecialMobileWatchlist fatal

Catchable fatal error:  Argument 5 passed to Wikibase\ClientHooks::onSpecialWatchlistQuery() must be an array, none given in /usr/local/apache/common-local/php-1.21wmf12/extensions/Wikibase/client/WikibaseClient.hooks.php on line 311

Change-Id: Iff45dbd548cc53c3f18dec0eff257adcf5adf769