posix-pstat/istat() - bail early if iatt structure is NULL

[mykaul]

In some cases, we can return early - when iatt structure is NULL. Specifically, this happens when we call those functions in part of MAKE_INODE_HANDLE() macro - which in some cases is not using that structure.

This saves us few calls. Specifically, we do not need to fetch mdata xattr, which may save us from some lgetxattr() and such.

Updates: #1000 Signed-off-by: Yaniv Kaul [email protected]