wayland/pointer: Unset current surface during window drags
Commit d48129f5 broke the displaying of our own drag cursor during window drags, as now the window cursor is always used, even during stage grabs (window grabs are just a kind of stage grab).
To fix it, while not regressing on the intention of the other commit, unset the MetaWaylandPointer surface in case a window drag is active (instead of all kinds of grabs).
Fixes: d48129f5 ("wayland: Fix pointer cursor during Wayland grabs")
Closes: #3316 (closed)
Edited by Jonas Dreßler