Update boost_container.dart

lib/container/boost_container.dart

@@ -249,7 +249,7 @@ class BoostContainerState extends NavigatorState {
           .prePushRoute(name, uniqueId, params, route);
     }
 
-    if (multipleRouteMode) {
+    if (multipleRouteMode && routerHistory.isNotEmpty) {
       ContainerNavigatorObserver.bindContainerManager().willPush(route, routerHistory.last);
     }