DeliveryReceipt, err:null error

[khaing211]

when DeliveryReceipt is initialized by constructor

 public DeliveryReceipt(String messageId, int submitCount, int deliveredCount, DateTime submitDate, DateTime doneDate, byte state, int errorCode, String text)

, rawErrorCode is not set. As a result, when toShortMessage() is called, it yield incorrect "err:null" field

[jjlauer]

Looks like a nice find. Would you be willing to take a stab at a fix and submit a PR?

[khaing211]

Done.