Track velocity of velocityPointerId only if is present

In case of multiple events with 0 pointers down (not pressed) we may
have already removed the velocityPointer.

Test: Rerun: atest MultiPointerDraggableTest
Bug: 367175475
Flag: com.android.systemui.scene_container
Change-Id: I8ee2030ec6154d844e994fe83a873e9a5910cd00