SystemUI: Fix missing top task in recent panel

If preloadRecentTasksList was not called or was called too
late and RecentsActivty already started and last top activity has
excludeFromRecents flag setted it might be missing
from recent application list.

atken from cm11

Change-Id: Ia04913e7a89d51689f933cbc9ff3a84092fdb1cf
[Patch 4] SystemUI: Fix missing top task in recent panel

If preloadRecentTasksList was not called or was called too
late and RecentsActivty already started and last top activity has
excludeFromRecents flag setted it might be missing
from recent application list.
atken from cm11

Link: https://gerrit.omnirom.org/#/c/6561/