Fix of my previous commit.

src/slic3r/GUI/GLCanvas3D.cpp

@@ -3941,12 +3941,14 @@ void GLCanvas3D::reload_scene(bool refresh_immediately, bool force_full_scene_re
                 mvs->volume_idx = glvolumes_new.size();
                 glvolumes_new.emplace_back(volume);
                 // Update color of the volume based on the current extruder.
+				if (mvs->model_volume != nullptr) {
 					int extruder_id = mvs->model_volume->extruder_id();
 					if (extruder_id != -1)
 						volume->extruder_id = extruder_id;
 				}
             }
         }
+    }
 
     if (m_reload_delayed)
         return;