smb: client: add NULL check in automount_fullpath

page is checked for null in __build_path_from_dentry_optional_prefix
when tcon->origin_fullpath is not set. However, the check is missing when
it is set.
Add a check to prevent a potential NULL pointer dereference.

Signed-off-by: Ruben Devos <[e-mail]>
Cc: [e-mail]
Signed-off-by: Steve French <[e-mail]>

fs/smb/client/namespace.c

···
 	}
 	spin_unlock(&tcon->tc_lock);
 
+	if (unlikely(!page))
+		return ERR_PTR(-ENOMEM);
+
 	s = dentry_path_raw(dentry, page, PATH_MAX);
 	if (IS_ERR(s))
 		return s;