FTS transfers may be submitted with incorrect source

The `filterReplicas` method [1] of `ReplicateAndRegister` checks the existing replicas of a file before replication. It performs physical checks, which means it can detect corrupted/missing files.

Unfortunately, that information is only ever used to avoid useless replication to existing targets.

This means that upon submission of the FTS job, we can still pick that bad replicas as source.

To be seen what can be done to avoid that...

[1] https://github.com/DIRACGrid/DIRAC/blob/959bf09c77bc64d54db7159b17878a362dc13b52/src/DIRAC/DataManagementSystem/Agent/RequestOperations/ReplicateAndRegister.py#L49