Slim Recents: fix multiwindow glitch when docking app to bottom

aosp multiwindow has this limitation, but we can easly bypass it
just docking first the app we want to top, then the bottom one

to replicate the issue:
open the recents panel
drag card1 below card2, to dock card1 on bottom and card2 on top
press home button

Change-Id: I24d8e7c0cfbe719f96c9ae8ffac2cc5ac958543f