If `unix.Lgetxattr` returns an error, then `sz == -1` which will cause a
runtime panic if `errno == unix.ERANGE`.
Signed-off-by: Sascha Grunert <sgrunert@suse.com>
(cherry picked from commit 4138cd22ab)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>