DoubleSlider: Implemented code for check of used extruders for MustiAsSingle mode

src/libslic3r/Print.hpp

@@ -382,6 +382,7 @@ public:
 
     // Accessed by SupportMaterial
     const PrintRegion*  get_region(size_t idx) const  { return m_regions[idx]; }
+    const ToolOrdering& get_tool_ordering() const { return m_wipe_tower_data.tool_ordering; }   // #ys_FIXME just for testing
 
 protected:
     // methods for handling regions