UnreadWikis: Check the actual object we're about to call a method on
UnreadWikis: Check the actual object we're about to call a method on

In principle, if $alertCount > 0, $alertTime should never be null,
but it feels much safer to check $alertTime itself instead.

Change-Id: Ifb107e257fbcd65e8181e2a214028f1b3733ac30

wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo