determine screenArea by geom_restore in checkWSP

checkWorkspacePosition() operates on geom_restore
to preserve window positions on temporary
(without moving/resizing the window by the user)
screen layout/geometry changes.

Therefore, in the multiscreen case the
screenbound check must be done towards
the screen the window *would* be on
according to geom_restore, not the one
it is right now.

CCBUG: 161325
REVIEW: 121320
FIXED-IN: 5.2