Fix Opening Maximized Media

Make sure the Image and Video Components can correctly get the index for opening the Maximize Media component.

src/timeline/ImageComponent.qml

@@ -21,6 +21,11 @@ Item {
      */
     required property NeoChatRoom room
 
+    /**
+     * @brief The index of the delegate in the model.
+     */
+    required property var index
+
     /**
      * @brief The matrix ID of the message event.
      */