fixed bug in load_and_merge() when using --cache_method=build_cache_all
fixed bug in load_and_merge() when using --cache_method=build_cache_all

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