message: Interaction.getPointerIndex: always -1 if unknown
  If it's a mouse interaction and the mouse pointer wasn't added yet,
  return -1 instead of always 0.
diff: @@ -314,7 +314,7 @@ class Interaction {
  }
  getPointerIndex (pointer) {
  - return this.mouse? 0 : utils.indexOf(this.pointerIds, utils.getPointerId(pointer));
  + return utils.indexOf(this.pointerIds, utils.getPointerId(pointer));
  }
  updatePointer (pointer, event, down = event && /(down|start)$/i.test(event.type)) {
  