Gracefully handle verification events that are unknown locally (#90)

src/worker.rs

@@ -845,11 +845,12 @@ impl ClientWorker {
                     let request = client
                         .encryption()
                         .get_verification_request(&ev.sender, &ev.content.transaction_id)
-                        .await
+                        .await;
-                        .unwrap();
 
+                    if let Some(request) = request {
                         request.accept().await.unwrap();
                     }
+                }
             },
         );