The previous implementation would pass the mouse wheel event up to the
component's parent, as long as the parent was enabled. This meant that a
wheel event on the innermost component of a hierarchy such as
"[[disabled] enabled]" would send the event to the parent, but a wheel
event on the innermost component of a hierarchy such as
"[[[disabled] disabled] enabled]" would 'eat' the event and prevent it
from propagating.

After this change, unhandled mouse wheel events will always be passed to
the nearest enabled parent. This behaviour is more consistent and
intuitive.