Simplify call to matomo.track()

See issue #29

packages/app-shell/src/app-shell.js

@@ -61,6 +61,7 @@ export class AppShell extends ScopedElementsMixin(LitElement) {
 
         this.matomoUrl = '';
         this.matomoSiteId = -1;
+        this.matomo = null;
 
         this._attrObserver = new MutationObserver(this.onAttributeObserved);
     }
@@ -255,6 +256,10 @@ export class AppShell extends ScopedElementsMixin(LitElement) {
         this.initRouter();
 
         this._bus.subscribe('auth-update', this._updateAuth);
+
+        this.updateComplete.then(()=> {
+            this.matomo = this.shadowRoot.querySelector(this.constructor.getScopedTagName('dbp-matomo'));
+        });
     }
 
     disconnectedCallback() {
@@ -668,9 +673,8 @@ export class AppShell extends ScopedElementsMixin(LitElement) {
     }
 
     track(action, message) {
-        const matomo = this.shadowRoot.querySelector(this.constructor.getScopedTagName('dbp-matomo'));
-        if (matomo !== null) {
-            matomo.track(action, message);
+        if (this.matomo !== null) {
+            this.matomo.track(action, message);
         }
     }