Check if we have a service worker available before trying to communicate with it

src/App.vue

@@ -329,13 +329,15 @@
 			// Service worker communication
 			document.addEventListener(swEvents.SW_UPDATED, this.showRefreshUI, {once: true})
 
+			if (navigator && navigator.serviceWorker) {
 				navigator.serviceWorker.addEventListener(
 					'controllerchange', () => {
 						if (this.refreshing) return;
 						this.refreshing = true;
 						window.location.reload();
 					}
-			);
+				)
+			}
 
 			// Try renewing the token every time vikunja is loaded initially
 			// (When opening the browser the focus event is not fired)