Bulk computation should not fail when the bulk command does not exist

The bulk command is retrieved from the KV store and if a record points to an unexisting command we stop the processing.

A command is removed from the KV store:

• when the command is completed normally and the TTL is 1h
• the command is completed in failure, the TTL for the command is 24h
• the KV store has been flushed

A computation may not found a command if its position has been manually set.

In such a case, it doesn't make sense to raise a stream failure and stop the processing, it is better to warn and skip the record as we cannot do anything to restore the command in the KV store.