Keep app when opening floating window from recents panel

Start activity asynchronously by appending it to system's
message queue to let RecentsPanelView cleanly execute
dismissAndGoBack before the floating window gets started.

Change-Id: Ie9c74b9f0b39f3aee81c62246cdcae15de83ee0d
Avoid SystemUI crash due to NPE

BaseStatusBar.createNotificationViews() returns null
when it reports handleNotificationError(), leading to
a forced crash of the misbehaving app. However, it
should not add a null object of Notification.Entry
since it will also crash SystemUI (crashing at compare).

Change-Id: I86678c8024e931420b0fbab1f36b330e7e75d581
Signed-off-by: houst0nn <houstonn@gmail.com>