Drain the requests already on the wire before close() and unbind() tear down

src/incoming-requests.ts

@@ -70,7 +70,7 @@ export class IncomingRequests {
 				break;
 			case 'unbind':
 				await this.session.sendReturn(pduObj);
-				this.session.close();
+				await this.session.close();
 				break;
 			default:
 				await this.unhandled(pduObj);