Add check for loading ever applied in check for page scrolls initialized

When "Don't keep activities" is enabled in developer settings, the RecentsView gets re-initialized every home gesture. The home animation can often finish before the load plan ever gets applied, so the page scrolls can be used before the RecentsView has had a chance to add all its TaskViews and recalculate its page scroll.

Fixes: 249020573
Test: launched an app and went home
Change-Id: I83ca9de60b50693f7a22b08534ec36973cd6a0fc