Unhelpful error when specifying :one but not including a RETURNING clause

```
-- name: DeleteFoo :one
DELETE FROM foo
WHERE id = $1 and type = $2;
```

Observed:
```
sqlc generate
# package query
error generating code: template: table:33:77: executing "table" at <.Ret.Type>: error calling Type: no type for GoQueryValue:
```

Expected:
"Query 'DeleteFoo' specifies parameter ":one" without containing a RETURNING clause"