Handle problem edge cases at starts of chromosomes
Handle problem edge cases at starts of chromosomes

CNVkit events at the end of chromosomes can start with 0, which
creates invalid BED causing downstream failures. This checks
for that edge case.

mjafin/bcbio-nextgen,brainstorm/bcbio-nextgen,lpantano/bcbio-nextgen,Cyberbio-Lab/bcbio-nextgen,lbeltrame/bcbio-nextgen,vladsaveliev/bcbio-nextgen,lpantano/bcbio-nextgen,chapmanb/bcbio-nextgen,guillermo-carrasco/bcbio-nextgen,lbeltrame/bcbio-nextgen,brainstorm/bcbio-nextgen,lpantano/bcbio-nextgen,a113n/bcbio-nextgen,gifford-lab/bcbio-nextgen,Cyberbio-Lab/bcbio-nextgen,gifford-lab/bcbio-nextgen,lbeltrame/bcbio-nextgen,elkingtonmcb/bcbio-nextgen,biocyberman/bcbio-nextgen,gifford-lab/bcbio-nextgen,vladsaveliev/bcbio-nextgen,vladsaveliev/bcbio-nextgen,Cyberbio-Lab/bcbio-nextgen,biocyberman/bcbio-nextgen,elkingtonmcb/bcbio-nextgen,biocyberman/bcbio-nextgen,elkingtonmcb/bcbio-nextgen,brainstorm/bcbio-nextgen,guillermo-carrasco/bcbio-nextgen,mjafin/bcbio-nextgen,chapmanb/bcbio-nextgen,a113n/bcbio-nextgen,guillermo-carrasco/bcbio-nextgen,mjafin/bcbio-nextgen,a113n/bcbio-nextgen,chapmanb/bcbio-nextgen