Gui: Fix disappearing element handles in sketcher

Finds the bounding sphere when the editing view provider is set. This ensures the right bounding sphere is used for finding the near and far clipping plane

src/Gui/View3DInventorViewer.cpp

@@ -1058,6 +1058,7 @@ void View3DInventorViewer::setEditingViewProvider(Gui::ViewProvider* vp, int Mod
 {
     this->editViewProvider = vp;
     this->editViewProvider->setEditViewer(this, ModNum);
+    this->navigation->findBoundingSphere();
     addEventCallback(SoEvent::getClassTypeId(), Gui::ViewProvider::eventCallback,this->editViewProvider);
 }