fix for register_all_chained where mid_cs is undef. i.e. mouse/rat etc
fix for register_all_chained where mid_cs is undef. i.e. mouse/rat etc

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