ISPN-4706 Don't abort Marshalling on interruption

The issue was identified via stress tests; I would hit it regularly and everything works much smoother with this fix.
The StressTest itself is not ready for merging yet.

 - https://issues.jboss.org/browse/ISPN-4706

@Sanne TBH I think it would also be ok to not clear the writers table on stop, but I don't want to introduce a leak so I added the proper stop check at the start of the method.