xattr: Fail with -EINVAL for NULL attribute names

Commit 98e9cb57 improved the xattr name checks in xattr_resolve_name but
didn't update the NULL attribute name check appropriately, so NULL
attribute names lead to NULL pointer dereferences.  Turn that into
-EINVAL results instead.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
  fs/xattr.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>