xattr: Remove unnecessary NULL attribute name check

When NULL is passed to one of the xattr system calls as the attribute
name, copying that name from user space already fails with -EFAULT;
xattr_resolve_name is never called with a NULL attribute name.

Signed-off-by: Andreas Gruenbacher <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>

fs/xattr.c

···
 {
 	const struct xattr_handler *handler;
 
-	if (!*name)
-		return ERR_PTR(-EINVAL);
-
 	for_each_xattr_handler(handlers, handler) {
 		const char *n;