No Error when invalid data is passed to a template

[tomfotherby]

Here is a test case:

    // Set a valid domain key
    Apostle::setup("valid-key-entered-here");

    // Create a mail instance. Ensure the mail template needs some data
    $mail = new Mail( "welcome", ["email" => "tom@example.com" ] );

    // Give some data but NOT what the template needs
    $mail->username = "Snikch";

    // Send to Apostle.io
    $result = $mail->deliver($failureMsg);

    echo $result ? "all ok" : "Something failed: $failureMsg\n";

It prints "all ok".

The apostle.io web-console shows the failure reason nicely:

Failed to hydrate template, check your template and data variables match

Would be better if we could get a error message from the API call saying the same message as the web-console gives us.