client: fix corner case of updating inline_version

handle following sequence of events:
 - A request reply brings inode to the client cache, but not together
   with inode cap. (The inode was frozen when MDS processed the request)
   The reply has empty inline data and zero inline_version.
 - Another request reply carries the inode's cap and up-to-date inline
   version/data. But the cached inode's version is equal to the reply's
   inode version.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>