Assert failure in bulk message parsing not caught
The RabbitmqRiver class has a try/catch around the parsing of the task's body into a BulkRequest. If this request is malformed, then the BulkRequest.add() method could fail with an assertion failure. This is not caught by the Exception.

Changing this to a catch(Throwable) allows the consumer to ack the message and move on to the next one.
Closes #14.