Check for Language::getSpecialPageAliases returning null in SpecialPageFactory

Language::getSpecialPageAliases can return null causing certain
methods within SpecialPageFactory that rely on it to raise
PHP warnings due to trying to foreach over a non-array.

This change will prevent the PHP warning from being raised and
allow those functions' error handling to occur normally.

Change-Id: I2026c25f12798f699ebc306b12173226270fce2e
Merge "Check for Language::getSpecialPageAliases returning null in SpecialPageFactory"