[Sketcher] Fix catching of rendering order change

model()->layoutChanged signal didn't work at all, was never emitted by widget
 Replaced with an eventFilter catching ChildRemoved to further emit the signal

src/Mod/Sketcher/Gui/TaskSketcherGeneral.cpp

@@ -36,6 +36,8 @@
 #include <Base/Tools.h>
 #include <Base/UnitsApi.h>
 
+#include <QEvent>
+
 #include "ViewProviderSketch.h"
 
 using namespace SketcherGui;
@@ -58,8 +60,7 @@ SketcherGeneralWidget::SketcherGeneralWidget(QWidget *parent)
             this, SLOT(onSetGridSize(double)));
     connect(ui->checkBoxAutoconstraints, SIGNAL(stateChanged(int)),
             this, SIGNAL(emitToggleAutoconstraints(int)));
-    connect(ui->renderingOrder->model(), SIGNAL(layoutChanged()),
-            this, SLOT(onRenderOrderChanged()));
+    ui->renderingOrder->installEventFilter(this);
 }
 
 SketcherGeneralWidget::~SketcherGeneralWidget()
@@ -67,6 +68,14 @@ SketcherGeneralWidget::~SketcherGeneralWidget()
     delete ui;
 }
 
+bool SketcherGeneralWidget::eventFilter(QObject *object, QEvent *event)
+{
+    if (object == ui->renderingOrder && event->type() == QEvent::ChildRemoved) {
+        onRenderOrderChanged();
+    }
+    return false;
+}
+
 void SketcherGeneralWidget::saveSettings()
 {
     ui->checkBoxShowGrid->onSave();

src/Mod/Sketcher/Gui/TaskSketcherGeneral.h

@@ -49,6 +49,8 @@ class SketcherGeneralWidget : public QWidget
 public:
     SketcherGeneralWidget(QWidget *parent=0);
     ~SketcherGeneralWidget();
+    
+    bool eventFilter(QObject *object, QEvent *event);
 
     void saveSettings();
     void saveOrderingOrder();