Don't copy lvb into reply message on error, since that message might not have

Don't copy lvb into reply message on error, since that message might not have
allocated enough space for the lvb and the client will ignore it anyways.
Also fixes a NULL request deref in mds_mfd_close() when cleaning up opens
on the MDS.  The initial sanity test (66b) triggered a new bug 2986, but
another test with multiop tests this properly.
b=2983