Don't trigger filter hits for nonexisting filter 0

AbuseFilter::getConsequencesForFilters uses filter ids as
array keys, that causes problems if both local and global
filters were hit, because array_merge reindexes arrays.

Example:
https://www.mediawiki.org/wiki/Special:AbuseLog/18687

Change-Id: I81cb110322461e30113199cfa313cd8e8e8b2262