server: libxtreemfs for Java: Quick fix for "already freed" assertion error when

retrying write requests.

The problem is that the RPC Client takes over the ownership of the data and
frees it although it's supposed to be used by subsequent retries.

Previous commit  41c8204689d1 with same intent was incomplete.

Conflicts:
	java/servers/src/org/xtreemfs/common/libxtreemfs/FileHandleImplementation.java