handle unknown non-api errors

[gabor]

if you check the error-handling logic, it goes roughly like this:

	if err != nil {
		if apiErr, ok := err.(*googleapi.Error); ok {
                         // handle api error
		}
	}

        // process the result

so, if we have an error, that is not an api-error, we just don't handle it at all, and we continue processing the result (even though we have an error).

this PR simply adds an else branch to handle non-api errors.

how to test:

1. run a google-sheets query, make sure it works
2. turn off the internet on your laptop 😁 , and repeat the query
3. you should see the error message "unknown error" (in main-branch at this point you'll see An error occurred within the plugin )