Fix album drag-drop when you drag by the thumbnail or other child.

frontends/etiquette_flask/templates/album.html

@@ -395,9 +395,25 @@ function create_child(title)
     api.albums.create(title, parent_id, api.albums.callback_follow);
 }
 
+function get_album_card_from_child(element)
+{
+    /*
+    Given an element which is known to be a child of an album card, navigate up
+    the parent tree until we find that album card.
+    This is used to make drag-and-drop work even when you start your drag by
+    clicking on the album's thumbnail, title, etc.
+    */
+    while (! element.classList.contains("album_card"))
+    {
+        element = element.parentElement;
+    }
+    return element;
+}
+
 function on_album_drag_start(event)
 {
-    event.dataTransfer.setData("text/plain", event.target.id);
+    let album_card = get_album_card_from_child(event.target);
+    event.dataTransfer.setData("text/plain", album_card.id);
 }
 function on_album_drag_end(event)
 {