Fix minor Editor UI issues

Source/Editor/Windows/Assets/ModelBaseWindow.cs

@@ -117,9 +117,12 @@ namespace FlaxEditor.Windows.Assets
 
             public override void OnClean()
             {
-                Window._isolateIndex = -1;
-                Window._highlightIndex = -1;
-                Window._meshProxy = null;
+                if (Window != null)
+                {
+                    Window._isolateIndex = -1;
+                    Window._highlightIndex = -1;
+                    Window._meshProxy = null;
+                }
 
                 base.OnClean();
             }

Source/Engine/UI/GUI/ContainerControl.cs

@@ -171,6 +171,12 @@ namespace FlaxEngine.GUI
         /// </summary>
         public virtual void DisposeChildren()
         {
+            // Steal focus from children to maintain it in a hierarchy
+            if (ContainsFocus)
+            {
+                Focus();
+            }
+
             bool wasLayoutLocked = _isLayoutLocked;
             _isLayoutLocked = true;