Show ThumbnailComponent as fallback instead of a MediaViewerImageComponent placeholder when only one of the mediaviewers options is enabled

Author: alexandrevryghem

src/app/item-page/media-viewer/media-viewer.component.html

@@ -16,9 +16,12 @@
     </ng-container>
   </div>
   <ng-template #showThumbnail>
-    <ds-media-viewer-image
+    <ds-media-viewer-image *ngIf="mediaOptions.image && mediaOptions.video"
       [image]="(thumbnailsRD$ | async)?.payload?.page[0]?._links.content.href || thumbnailPlaceholder"
       [preview]="false"
     ></ds-media-viewer-image>
+    <ds-thumbnail *ngIf="!(mediaOptions.image && mediaOptions.video)"
+                  [thumbnail]="(thumbnailsRD$ | async)?.payload?.page[0]">
+    </ds-thumbnail>
   </ng-template>
 </ng-container>