Fixed consistent flicker on shade open after multitouch

Bug was triggered by skipped ACTION_DOWN after multitouch breaking
the shade. The flicker was caused by mTracking not being properly set,
and the mInitialExpandY not being reset from the previous gesture
caused the shade to require a much longer swipe to begin expanding.

Bug: 264665511
Test: manual
Change-Id: I9a1a93d9661d6c3cd69356883e12a04010641d3b