Report samples with zero variants in svtk count-svtypes

[RCollins13]

The default behavior of svtk count-svtypes appears to only report samples with at least one variant present in the VCF, and thus does not report samples present in the VCF header but lacking any variants in the file.

Can you add an option (or make it the default) to output counts of SV for all samples present in the VCF header, even if they have no observed variants?

This will be a useful feature for quick QC.

Thanks!