Scroll wheel events trigger from mouse movement

[adamzl]

Issue: If you set an Action to have a Binding to scroll/y the mouse position movement will cause previous scroll wheel inputs to re-fire.

Reproduction:

1. New Action Map, new Action.
2. Add Binding
3. Path = Mouse -> Scroll -> Y
4. Debug.Log the triggered callback.

Observe that initially moving the mouse position does nothing, use the scroll wheel and observe callbacks. Then move the mouse position after having use the scroll wheel and observe more callbacks.

[douglas-piconi]

This bug has been fixed and is available in the following versions of the editor.

2019.1.5f1 and greater
2019.2.0b2 and greater
2019.3.0a3 and greater