Continue loading visible task data when scrolling recents during anim to home

When we go from overview to home, we scroll to page 0 so that all tasks end up offscreen. However, since we are already in NORMAL state, we previously ignored loadVisibleTaskData() for the tasks as they scrolled by. Instead, we now continue loading task data while the scroller is unfinished.

Test: swipe to last recent task, swipe up to home, ensure thumbnails are still loaded as they scroll offscreen
Bug: 192522519
Change-Id: Iba770200fc5dbdfc91dccda9a6b9c891ab6c5e3d