on exit of hyprland the CMonitor destroy signal comes after the
compositor has been destructed, causing a heap use after free. add if
check to ensure compositor exist and isnt shutting down when its
triggered.
When `region_size` is set in the config (non-empty
`boundBox`), cursor is mapped to wrong coordinate because
`CBox::translate` mutates `TAB->boundBox`, making all subsequent coordinate
calculations wrong.
This also fixes the edge case where user sets `region_position` but
not `region_size`.
