message: check if pointer actually moved
diff: import { Subject, Observable } from 'rxjs';
  -import { Vec2 } from '../../mol-math/linear-algebra';
  +import { Vec2, EPSILON } from '../../mol-math/linear-algebra';
  import { BitFlags, noop } from '../../mol-util';
  @@ -474,6 +474,7 @@ namespace InputObserver {
  if (dragging === DraggingState.Stopped) return
  Vec2.div(pointerDelta, Vec2.sub(pointerDelta, pointerEnd, pointerStart), getClientSize(rectSize))
  + if (Vec2.magnitude(pointerDelta) < EPSILON) return
  const isStart = dragging === DraggingState.Started
  const [ dx, dy ] = pointerDelta
  