Edge case for high depth variant filter
Edge case for high depth variant filter

Handle empty VCF cases where we have no variants with depth set
for filtering on

vladsaveliev/bcbio-nextgen,lbeltrame/bcbio-nextgen,a113n/bcbio-nextgen,chapmanb/bcbio-nextgen,biocyberman/bcbio-nextgen,a113n/bcbio-nextgen,lbeltrame/bcbio-nextgen,a113n/bcbio-nextgen,mjafin/bcbio-nextgen,brainstorm/bcbio-nextgen,mjafin/bcbio-nextgen,lbeltrame/bcbio-nextgen,brainstorm/bcbio-nextgen,brainstorm/bcbio-nextgen,biocyberman/bcbio-nextgen,vladsaveliev/bcbio-nextgen,vladsaveliev/bcbio-nextgen,biocyberman/bcbio-nextgen,mjafin/bcbio-nextgen,chapmanb/bcbio-nextgen,chapmanb/bcbio-nextgen