o Minor bugfixes (client):
    - Check for a missing option value in parse_virtual_addr_network
      before asserting on the NULL in tor_addr_parse_mask_ports.
      This avoids crashing on torrc lines like
      Vi[rtualAddrNetworkIPv[4|6]] when no value follows the option.
      Fixes bug 14142; bugfix on 0.2.4.7-alpha.
      Patch by "teor".