Guard against null pointer access

Author: githubuser0xFFFF

src/DockAreaWidget.cpp

@@ -452,6 +452,11 @@ void CDockAreaWidget::insertDockWidget(int index, CDockWidget* DockWidget,
 void CDockAreaWidget::removeDockWidget(CDockWidget* DockWidget)
 {
     ADS_PRINT("CDockAreaWidget::removeDockWidget");
+    if (!DockWidget)
+    {
+    	return;
+    }
+
     auto CurrentDockWidget = currentDockWidget();
   	auto NextOpenDockWidget = (DockWidget == CurrentDockWidget) ? nextOpenDockWidget(DockWidget) : nullptr;