Following up on CL 403694, there is a bit of confusion about
when Path is and isn't set, along with now the exported Err field.
Catch the case where Path and Err (and lookPathErr) are all unset
and give a helpful error.
Followup after #43724.
Reviewed-by: Bryan Mills <firstname.lastname@example.org>
Reviewed-by: Roland Shoemaker <email@example.com>
(cherry picked from commit 960ffa9)
Run-TryBot: Roland Shoemaker <firstname.lastname@example.org>
TryBot-Result: Gopher Robot <email@example.com>