Let's keep starting the timer for the retries straight away

rather than leaving them until next time the queue is sent

src/crypto/OutgoingRoomKeyRequestManager.js

@@ -302,6 +302,7 @@ export class OutgoingRoomKeyRequestManager {
                                 "Error sending room key request cancellation;"
                                 + " will retry later.", e,
                             );
+                            this._startTimer();
                         });
                     });
                 }