Fix parsing failure for NFSv4 Setattr operation for failed case.

If an operation that preceeds a Setattr in an NFSv4 compound fails,
there is no bitmap of attributes to parse. Without this patch, the
parsing would fail and return EBADRPC instead of the correct failure
error. This could break recovery from a server crash/reboot.

Tested by: cperciva
PR: 215883
MFC after: 2 weeks