Fix npe on setSquishinessFraction

NPE originally being thrown because of race condition between the
notification panel dismissal animation and the layout path; fixed by
waiting for layout path to be populated before using it

Test: atest QSPanelTest
Fixes: 242139605
Change-Id: Ib1f0f90d27b15d838199390f87198eb5c0988dc5
2 files changed