Add auto-expand for items list with a single category in use

Source/Editor/GUI/ItemsListContextMenu.cs

@@ -52,7 +52,7 @@ namespace FlaxEditor.GUI
             public float SortScore;
 
             /// <summary>
-            /// Wether the query highlights should be draw.
+            /// Whether the query highlights should be drawn.
             /// </summary>
             public bool DrawHighlights = true;
 
@@ -261,6 +261,11 @@ namespace FlaxEditor.GUI
         /// </summary>
         public readonly VerticalPanel ItemsPanel;
 
+        /// <summary>
+        /// Gets a list of panels with item categories.
+        /// </summary>
+        public IEnumerable<DropPanel> CategoryPanels => (IEnumerable<DropPanel>)_categoryPanels ?? Array.Empty<DropPanel>();
+
         /// <summary>
         /// Initializes a new instance of the <see cref="ItemsListContextMenu"/> class.
         /// </summary>
@@ -504,6 +509,12 @@ namespace FlaxEditor.GUI
                     category.Visible = true;
                     category.Close(false);
                 }
+
+                if (_categoryPanels.Count == 1 && items.Count == 1)
+                {
+                    // Expand the only category if there are no items outside of it
+                    _categoryPanels[0].Open(false);
+                }
             }
 
             _searchBox?.Clear();