Apparmor: Use d_is_positive/negative() rather than testing dentry->d_inode

Use d_is_positive(dentry) or d_is_negative(dentry) rather than testing
dentry->d_inode as the dentry may cover another layer that has an inode when
the top layer doesn't or may hold a 0,0 chardev that's actually a whiteout.

Signed-off-by: David Howells <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>

security/apparmor/path.c

···
 	 *    security_path hooks as a deleted dentry except without an inode
 	 *    allocated.
 	 */
-	if (d_unlinked(path->dentry) && path->dentry->d_inode &&
+	if (d_unlinked(path->dentry) && d_is_positive(path->dentry) &&
 	    !(flags & PATH_MEDIATE_DELETED)) {
 			error = -ENOENT;
 			goto out;