Prevent integer overflow while parsing long strings.

src/lj_lex.c

@@ -140,7 +140,7 @@ static int skip_sep(LexState *ls)
   int s = ls->current;
   lua_assert(s == '[' || s == ']');
   save_and_next(ls);
-  while (ls->current == '=') {
+  while (ls->current == '=' && count < 0x20000000) {
     save_and_next(ls);
     count++;
   }