Skip picking pass when plater is empty

src/slic3r/GUI/GLCanvas3D.cpp

@@ -1356,7 +1356,7 @@ void GLCanvas3D::render()
         if (m_rectangle_selection.is_dragging())
             // picking pass using rectangle selection
             _rectangular_selection_picking_pass();
-        else
+        else if (!m_volumes.empty())
             // regular picking pass
             _picking_pass();
     }