Update SearchProvider.php

[devgrunge]

Added an extra validation at $queryType to avoid errors while overriding the faceted search module

Questions	Answers
Description?	This change was made to the SearchProvider class, to make it possible to add new fields or change the order of the order-by field without throwing exceptions or errors, validating that the queryType variable is not null
Type?	Improvement
BC breaks?	Yes
Deprecations?	Yes
Fixed ticket?	No.
How to test?	Doing an override of this class and adding new sorting options