Fix crash when selecting an object

issue no. 11

src/slic3r/GUI/GLCanvas3D.cpp

@@ -7055,5 +7055,18 @@ void GLCanvas3D::GizmoHighlighter::blink()
         invalidate();
 }
 
+const ModelVolume *get_model_volume(const GLVolume &v, const Model &model)
+{
+    const ModelVolume * ret = nullptr;
+
+    if (model.objects.size() < v.object_idx()) {
+        const ModelObject *obj = model.objects[v.object_idx()];
+        if (obj->volumes.size() < v.volume_idx())
+            ret = obj->volumes[v.volume_idx()];
+    }
+
+    return ret;
+}
+
 } // namespace GUI
 } // namespace Slic3r

src/slic3r/GUI/GLCanvas3D.hpp

@@ -1046,6 +1046,8 @@ private:
     float get_overlay_window_width() { return LayersEditing::get_overlay_window_width(); }
 };
 
+const ModelVolume * get_model_volume(const GLVolume &v, const Model &model);
+
 } // namespace GUI
 } // namespace Slic3r
 

src/slic3r/GUI/Selection.cpp

@@ -1974,8 +1974,8 @@ std::vector<unsigned int> Selection::get_volume_idxs_from_instance(unsigned int
 
     for (unsigned int i = 0; i < (unsigned int)m_volumes->size(); ++i) {
         const GLVolume* v = (*m_volumes)[i];
-        if (pt == ptSLA && v->is_modifier &&
+        const ModelVolume *mv = get_model_volume(*v, *m_model);
-            m_model->objects[object_idx]->volumes[i]->is_modifier())
+        if (pt == ptSLA && v->is_modifier && mv && mv->is_modifier())
             continue;
         if (v->object_idx() == (int)object_idx && v->instance_idx() == (int)instance_idx)
             idxs.push_back(i);