Mouse wheel behavior in offset canvas

[jwdunn1]

View a reproduction of the issue here In this example, the red zone represents a non-offset canvas. The mouse wheel only works (zooms) where the red overlaps the offset canvas. The wheel fails while over the canvas outside the red zone. Expected behavior: mouse wheel should work if the mouse pointer is anywhere over the canvas, even when offset. Code at line 299 should account for canvas offset in a manner similar to the handling of mousedown and dblclick.