Cast up to get rid of the potential overflow posibility

regcomp.c

@@ -5034,7 +5034,7 @@ optimize_node_left(Node* node, NodeOptInfo* opt, OptEnv* env)
 
 	if (NSTRING_IS_DONT_GET_OPT_INFO(node)) {
 	  int n = onigenc_strlen(env->enc, sn->s, sn->end);
-	  max = ONIGENC_MBC_MAXLEN_DIST(env->enc) * n;
+	  max = ONIGENC_MBC_MAXLEN_DIST(env->enc) * (OnigDistance)n;
 	}
 	else {
 	  concat_opt_exact_info_str(&opt->exb, sn->s, sn->end,