[pdal] pdal ground options '--max_window_size' and '--approximate'

[FE]

Hi,

I've detected that pdal ground does not accept values smaller than 1.0 for option '--max_window_size'.

Further when using the option '--approximate' other options like '--max_window_size' are completely ignored. In such case always the standard values of max_window_size are used.

Thanks for help!