Fix a maximized X11 window overhanging the screen by its own border

Reported by the aegis-fc peer session testing srdwm's own layer-shell
strut handling: a maximized X11 client sat 4-8px past the right and
bottom screen edges whenever its border was nonzero.

set_border_width sets the frame's native X11 border-width attribute,
which the X server draws outside a window's own declared width/height on
all four sides - unlike every other backend's own border in this
compositor (rendered as ordinary pixels inside the allocated geometry
rect). apply_geometry configured the frame at geometry's own x/y/width/
height verbatim, so a nonzero native border pushed the frame's true
visible footprint 2*border_width past every edge of what geometry
actually promised.

Fixed by shifting the configured origin inward and the configured size
down by border_width on both axes (frame_geometry_for, pulled out as a
pure function so it's unit-tested without a real X11 connection) - the
visible footprint, native border included, now lands exactly on
geometry. border_width == 0 reduces to the prior behavior exactly.

0 files changed, 0 insertions, 0 deletions