Fixed bug in node removal - the removed node was left in invalid state.

This only caused problems if the node was later added back.

src/Libraries/SharpTreeView/ICSharpCode.TreeView/FlatListTreeNode.cs

@@ -364,6 +364,8 @@ namespace ICSharpCode.TreeView
 			Debug.Assert(node.listParent == null);
 			Debug.Assert(node.left == null);
 			Debug.Assert(node.right == null);
+			node.height = 1;
+			node.totalListLength = -1;
 			if (balancingNode != null)
 				RebalanceUntilRoot(balancingNode);
 		}