Fix router initialization in eventhandler

useRouter has to be called in setup or returns undefined otherwise.
See https://github.com/vuejs/vue-router/issues/3379

web/src/pages/Login.vue

@@ -5,6 +5,7 @@ import { useSessionStore } from "../stores/session";
 
 const error = ref("");
 const login = ref({ user: "", password: "" });
+const router = useRouter(); // has to be called in setup
 
 onMounted(() => {
     useSessionStore().setTitle("Login");
@@ -15,7 +16,8 @@ function formSubmit(e: MouseEvent) {
     useSessionStore().login(login.value)
         .then(x => {
             error.value = "";
-            useRouter().replace("/dashboard");
+            router.replace("/dashboard");
+            return x;
         })
         .catch(x => error.value = "The entered credentials are invalid!");