Revert "Avoid loading children when they aren't needed."

This reverts commit 56faf46597.
The commit was causing issues with treeview filtering (e.g. Resources node not visible).

ILSpy/TreeNodes/ILSpyTreeNode.cs

@@ -157,8 +157,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 		
 		void EnsureChildrenFiltered()
 		{
-			// No need to ensure lazy children here:
-			// if the children get lazy-loaded later, they'll still be filtered.
+			EnsureLazyChildren();
 			if (childrenNeedFiltering) {
 				childrenNeedFiltering = false;
 				foreach (ILSpyTreeNode node in this.Children.OfType<ILSpyTreeNode>())