__ocfs2_add_entry(), ocfs2_prepare_dir_for_insert(): namelen checks

namelen can't be zero; neither when it's coming from dentry name,
nor when dealing with orphans (in ocfs2_orphan_add() and
__ocfs2_prepare_orphan_dir()).  Rudiment of old ext2 pointless
check, long gone in ext2 itself...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>