Update uses of ParserOutput::getPageProperty() to handle new return value
Update uses of ParserOutput::getPageProperty() to handle new return value

The return value of ParserOutput::getPageProperty() will transition to
returning `null` instead of `false` when the page property is missing.

Bug: T301915
Change-Id: I79f9f4078e415284af29b15047bafd1c823d7f5b

wikimedia/mediawiki-extensions-PageTriage,wikimedia/mediawiki-extensions-PageTriage,wikimedia/mediawiki-extensions-PageTriage