Use correct bounds when calculating systemui visibility

currently the organizer-created primary split root-task always
populates the split-screen primary stack reference, so
isSplitScreenModeActivated needs to be used, instead, to check
if we are in split-screen

Bug: 152462949
Test: used log-statements to verify that it thinks split is false
Change-Id: I3a762bfdb323c530d60bc15043a12cb3d456a722