The `clientgen` utility doesn't work with just `--version` or `--help`

[wravery]

Both of them report a missing required parameter:

Command line errror: the option 'schema' is required but missing
Usage:  clientgen [options] <schema file> <request file> <output filename prefix> <output namespace>
Command line options:
  --version              Print the version number
  -? [ --help ]          Print the command line options
  -v [ --verbose ]       Verbose output including generated header names as
                         well as sources
  -s [ --schema ] arg    Schema definition file path
  -r [ --request ] arg   Request document file path
  -o [ --operation ] arg Operation name if the request document contains more
                         than one
  -p [ --prefix ] arg    Prefix to use for the generated C++ filenames
  -n [ --namespace ] arg C++ sub-namespace for the generated types
  --source-dir arg       Target path for the <prefix>Client.cpp source file
  --header-dir arg       Target path for the <prefix>Client.h header file
  --no-introspection     Do not expect support for Introspection