Without the change build fails on `ncurses-6.5` with opaque WINDOW as:
aacurses.c: In function 'curses_getsize':
aacurses.c:74:20: error: invalid use of incomplete typedef 'WINDOW' {aka 'struct _wi
n_st'}
74 | *width = stdscr->_maxx + 1;
| ^~
The change uses `gemaxx()` / `getmaxy()` instead.