ENSCORESW-1349: return slice if no offset
ENSCORESW-1349: return slice if no offset

muffato/ensembl,james-monkeyshines/ensembl,Ensembl/ensembl,muffato/ensembl,james-monkeyshines/ensembl,danstaines/ensembl,Ensembl/ensembl,danstaines/ensembl,james-monkeyshines/ensembl,james-monkeyshines/ensembl,Ensembl/ensembl,Ensembl/ensembl,danstaines/ensembl,muffato/ensembl,muffato/ensembl