Vue: fix component destroy error

src/VueChartwerkPodMixin.ts

@@ -32,7 +32,9 @@ export default {
     this.renderChart();
   },
   destroyed() {
-    this.pod.removeEventListeners();
+    if(this.pod) {
+      this.pod.removeEventListeners();
+    }
     this.pod = undefined;
   },
   methods: {