set s_score to 0 if not exists

dabo/functions/score.sh

@@ -1,4 +1,5 @@
 function score {
+  [ -z "${s_score}" ] && s_score=0
   #s_score=$((s_score${1}))
   g_calc "${s_score} + ${1}"
   s_score=${g_calc_result}