Protect against NaN in flyout collapses.

This can happen if getWidth() returns 0, likely the result of a race condition. Since
setFlyoutCollapsed is called continuously as a flyout is dragged, we can just wait
until getWidth() > 0.

Bug: 139816141
Test: atest SystemUITests
Change-Id: I2e7b8521a2930564f71919f4f4708c791a9b3545