nfs4: Fix wrong parenthesising in ReplyInterpreter::_FlattenPathname

This patch solves CID 990966.
nfs4: Ensure that a string is NULL terminated after strncpy()

This fixes CID 990971.
nfs4: Fix CID 990984 and 991173: missing assignment in error check
nfs4: Fix error checking in NFS4Server::_Renewal()

This fixes CID 990985.
nfs4: Do not rely on implementation defined casting uint32 to int32

This solves CID 991172.
nfs4: Fix CID 991174: improve error checking in NFS4Inode::OpenFile()
nfs4: Fix CID 991246: use name of the old entry when reporting removal
nfs4: Fix CID 991294: error handling issues in Auth::CreateSys()
nfs4: Fix memory leaks in case of error in ReplyInterpreter::_DecodeAttrs()

This patch fixes CID 991505, 991504, 991502, 991500, 991499, 991496.