Optimizations: don't call fetch* if there are no IDs to fetch
Optimizations: don't call fetch* if there are no IDs to fetch

danstaines/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,danstaines/ensembl-compara,danstaines/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,danstaines/ensembl-compara,danstaines/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara