fix empty locale option when first created

When App component is created not using query parameter 'loc',
locale data is empty.
So add checking logic $route.query.loc

quiz-app/src/App.vue

@@ -38,7 +38,9 @@ export default {
     },
   },
   created() {
-    this.locale = this.$route.query.loc;
+    if (this.$route.query.loc) {
+      this.locale = this.$route.query.loc;
+    }
   },
 };
 </script>