Fix check of return value from SpecialPageFactory::resolveAlias

Calling SpecialPageFactory::resolveAlias with an invalid special page
name, gives an array( null, null ) back, but this part of code checks
explicit against !false, which gives always true. Changed the condition
to use an (implicit) check, like the other places, where
SpecialPageFactory::resolveAlias is called.

Change-Id: I8def9dd88ebfbe9fcf1ba8f9cae9e25039ec77ed