bignum.c: fix rb_cstr_parse_inum endp

* bignum.c (rb_cstr_parse_inum): stores the address of the first
  invalid character when str is too big or contains an underscore.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57269 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

bignum.c

@@ -4172,6 +4172,7 @@ rb_cstr_parse_inum(const char *str, ssize_t len, char **endp, int base)
     digits_start = str;
     if (!str2big_scan_digits(s, str, base, badcheck, &num_digits, &len))
 	goto bad;
+    if (endp) *endp = (char *)(str + len);
     digits_end = digits_start + len;
 
     if (POW2_P(base)) {