On Sender Key distribution message failure, don't update send status

ts/textsecure/Types.d.ts

@@ -251,6 +251,10 @@ export interface CallbackResultType {
   unidentifiedDeliveries?: Array<string>;
   dataMessage?: Uint8Array;
 
+  // If this send is not the final step in a multi-step send, we shouldn't treat its
+  //   results we would treat a one-step send.
+  sendIsNotFinal?: boolean;
+
   // Fields necessary for send log save
   contentHint?: number;
   contentProto?: Uint8Array;