Several functions write to
wlr_box output arguments, but do not
write to their x/y coordinates when setting the boxes to empty.
Unfortunately, the callers still access their x and y fields
afterward, expecting them to be initialized.
wlr_output_layout_get_box to fully initialize its box argument
manage to avoid actual undefined behavior here by handling the
wlr_box_empty(box) case specially, but it's much clearer and
safer for functions to not conditionally partially initialize
their output arguments.
Also found with