This function was mistakenly called with a MetaWindow as first
argument inside the ::position-changed callback, instead of a
MetaWindowActor as it should.
However, that function quickly grabs the MetaWindow from the
actor, and all calling places have the MetaWindow readily available,
so switch to handing it as first function parameter.
Fixes warnings on ::position-changed, because of the aforementioned
typo.
c8ea06be26