Fix fatal in mobileview

Fatal error:  Call to a member function isMainPage() on a non-object in
/usr/local/apache/common-local/php-1.24wmf10/extensions/MobileFrontend/includes/api/ApiMobileView.php
on line 270

Bug: 67164

Change-Id: Iee5a981c326cdc386c8785732da06bb9ef174d8d