games/cataclysm-dda: fix build
/wrkdirs/usr/ports/games/cataclysm-dda/work-curses/Cataclysm-DDA-0.H-g08f04fd/src/game.cpp:2872:42: error: variable 'slen' used in loop condition not modified in loop body [-Werror,-Wfor-loop-analysis]
2872 | for( int slen = vRip[iY].size(); slen > 0; ) {
| ^~~~