ext4_add_entry(): ->d_name.len is never 0

That bogosity goes back to the initial merge of ext3.  Once upon a time
ext2 used to have a similar check; that got taken out during the switch
to page cache (June 2001).  ext3 got merged into mainline 5 months later,
still using buffer cache for directories; removal of the pointless check
in ext2 should've been done as a separate patch, but it hadn't been,
so that thing got missed...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/ext4/namei.c

@@ -2388,8 +2388,6 @@ static int ext4_add_entry(handle_t *handle, struct dentry *dentry,
 
 	sb = dir->i_sb;
 	blocksize = sb->s_blocksize;
-	if (!dentry->d_name.len)
-		return -EINVAL;
 
 	if (fscrypt_is_nokey_name(dentry))
 		return -ENOKEY;