message: Prevent getDelta calls from continuing after closing delta manager
diff: @@ -73,6 +73,7 @@ export class DeltaManager extends EventEmitter implements runtime.IDeltaManager
  private connecting: Deferred<IConnectionDetails>;
  private connection: DeltaConnection;
  private clientSequenceNumber = 0;
  + private closed = false;
  private handler: IDeltaHandlerStrategy;
  private deltaStorageP: Promise<runtime.IDocumentDeltaStorageService>;
  @@ -257,6 +258,7 @@ export class DeltaManager extends EventEmitter implements runtime.IDeltaManager
  * Closes the connection and clears inbound & outbound queues.
  */
  public close() {
  + this.closed = true;
  this.stopHeartbeatSending();
  this.stopSequenceNumberUpdate();
  if (this.connection) {
  @@ -295,6 +297,9 @@ export class DeltaManager extends EventEmitter implements runtime.IDeltaManager
  allDeltas: runtime.ISequencedDocumentMessage[],
  deferred: Deferred<runtime.ISequencedDocumentMessage[]>,
  retry: number) {
  + if (this.closed) {
  + return;
  + }
  // Grab a chunk of deltas - limit the number fetched to MaxBatchDeltas
  const deltasP = this.deltaStorageP.then((deltaStorage) => {
  