'pass' based credential helper returns success when cred doesn't exist

[nicks]

Repro steps:

echo "garbage" | go run ./pass/cmd/main.go get

Expected: Exit code 1

Actual: Exit code 0 {"ServerURL":"garbage","Username":"","Secret":""}

This is the root of cryptic errors like:

WARNING: could not erase credentials: error erasing credentials - err: exit status 1, out: `exit status 1: Error: docker-credential-helpers/[CRED_FOLDER_NAME] is not in the password store.`