Fixing exception in "load layout". This exception is illegal for this case in “load layout” logic, because the “save layout” logic assumes such case

Author: hpsa

src/Libraries/AvalonDock/AvalonDock/DockingManager.cs

@@ -3754,7 +3754,7 @@ void RestoreLayout(XmlDocument doc)
                 throw new FileFormatException("Unsupported layout file version");
 
             if (doc.DocumentElement.ChildNodes.Count != 3 ||
-                (doc.DocumentElement.ChildNodes[0].Name != "ResizingPanel" && doc.DocumentElement.ChildNodes[0].Name != "DocumentPane") ||
+                (doc.DocumentElement.ChildNodes[0].Name != "ResizingPanel" && doc.DocumentElement.ChildNodes[0].Name != "DocumentPane" && doc.DocumentElement.ChildNodes[0].Name != "DocumentPaneResizingPanel") ||
                 doc.DocumentElement.ChildNodes[1].Name != "Hidden" ||
                 doc.DocumentElement.ChildNodes[2].Name != "Windows")
             {