handle features that only have seqnames (and no slices!)
handle features that only have seqnames (and no slices!)

muffato/ensembl,mjg17/ensembl,Ensembl/ensembl,mjg17/ensembl,danstaines/ensembl,mjg17/ensembl,james-monkeyshines/ensembl,james-monkeyshines/ensembl,at7/ensembl,at7/ensembl,danstaines/ensembl,muffato/ensembl,muffato/ensembl,at7/ensembl,james-monkeyshines/ensembl,muffato/ensembl,james-monkeyshines/ensembl,mjg17/ensembl,willmclaren/ensembl,willmclaren/ensembl,danstaines/ensembl,Ensembl/ensembl,Ensembl/ensembl,at7/ensembl,Ensembl/ensembl