Pass background color from transition info to remote animation

With shell transition, there won't be task info if the transition
is launching activity in the same task. ActivityLaunchAnimator
assumed the task info is non-null, which causes NPE.

Bug: 223397404
Test: adb shell setprop persist.wm.debug.shell_transit 1; reboot
      Long press quick settings tile from notification multiple
      time. Especially launch the same tile twice, systemui
      should not crash.
Change-Id: I0ad1fef17653d72162d430339ac7e8a716aa9bfe