Bugfix: Check for existence of a new transfer requires a remote-call

* The _local_ check for the existens of a transfer to create possibly leads
  to a NPE in this version, because it access the TransferRepository for a
  partition, not regarding, if it is available locally.
* This access simply lead to no result before, but since the in-memory
  maps for the partitions are now created only, when the partition is
  assigned, it causes a NPE now.
* The local check, that does not make a lot of sence since the service
  was refactored to run on multiple insances in parallel, is replaced
  against a remote call here.