lib/file: return -ENOENT for NULL token list lookups
lib/file: return -ENOENT for NULL token list lookups

An empty token list is NULL, so elasto_ftoken_find() should return
-ENOENT in such cases, rather than -EINVAL. This fixes location
tracking,

Signed-off-by: David Disseldorp <589a549dc9f982d9f46aeeb82a09ab6d87ccf1d8@suse.de>

ddiss/elasto,ddiss/elasto