message: Make epsilon transition conditional
diff: @@ -244,7 +244,7 @@ void read_ipv6_address(state<Iterator, Sentinel>& ps, Consumer& consumer) {
  // Stops parsing after reading "::" (all-zero address) or proceeds with
  // reading the suffix.
  term_state(has_sep) {
  - epsilon(rd_suffix)
  + epsilon(rd_suffix, hexadecimal_chars)
  }
  // Read part of the prefix, i.e., everything before "::".
  state(rd_prefix) {
  