MOBILE-3167 dashboard: Set fallback blocks visibility to true

src/core/courses/pages/dashboard/dashboard.ts

@@ -236,10 +236,12 @@ export class CoreCoursesDashboardPage implements OnDestroy {
     protected loadFallbackBlocks(): void {
         this.blocks = [
             {
-                name: 'myoverview'
+                name: 'myoverview',
+                visible: true
             },
             {
-                name: 'timeline'
+                name: 'timeline',
+                visible: true
             }
         ];
     }