Show at least basic error if task or app not found in logviewer

dashboard/src/logs.html

@@ -65,7 +65,8 @@
   <a class="offline-banner animateMe" ng-show="client.offline" ng-cloak href="https://docs.cloudron.io/troubleshooting/" target="_blank"><i class="fa fa-circle-notch fa-spin"></i> {{ 'main.offline' | tr }}</a>
 
   <div class="animateMe ng-hide layout-root" ng-show="initialized">
-    <div class="logs-controls">
+    <div ng-show="error" class="logs-error">{{ 'logs.notFoundError' | tr }}</div>
+    <div ng-hide="error" class="logs-controls">
       <h3 style="display: inline-block;">{{ selected.name }}</h3>
 
       <!-- logs actions -->