Disallow routing to departing station

src/main.rs

@@ -194,6 +194,10 @@ async fn route_station_to_dest_station(
         return Err((StatusCode::NOT_FOUND, String::from("Unknown destination station")));
     }
 
+    if dest_station_id == station_id {
+        return Err((StatusCode::NOT_FOUND, String::from("Cannot route to departing station as destination")));
+    }
+
     let station_properties = match state.stations.get(&station_id) {
         Some(v) => v,
         None => return Err((StatusCode::INTERNAL_SERVER_ERROR, String::from("Station properties for departing station missing"))),