nfs4: Fix CID 991506: memory leak in case of error
nfs4: check for presence of FATTR4_CHANGE is not required

This fixes CID 991501.
nfs4: Take advantage of strlcpy()
nfs4: Fix error handling issues in Inode::Open() and Inode::Create()

This fixes CID 991498.
nfs4: Remove RequestBuilder::ReadDir() count argument

The argument is ignored anyway. This fixes CID 991593.
nfs4: Fix memory leaks in case of errors while reading a directory

This fixes CID 991497.
nfs4: Remove check for presence of mandatory attributes

This fixes CID 991495.
nfs4: Fix CID 991752: remove unnecessary return