This applies a part of golang.org/cl/137075 to the fallback. If go list
doesn't find a package, it returns an almost empty package structure
with an error set on it. That change passed through those packages
from the 1.11+ go list, so users could determine there wasn't a match.
This change does the same from the go 1.10 fallback go list code.
Change-Id: I98acc186c0a9eeef0416e9fec0e1fe0e29ddc51c
Reviewed-on: https://go-review.googlesource.com/c/139158
Reviewed-by: Alan Donovan <adonovan@google.com>
cb0b336180