Wipe tower: don't do sparse infill when there is a soluble filament above it

src/libslic3r/GCode/WipeTower.hpp

@@ -183,6 +183,7 @@ public:
 
     struct FilamentParameters {
         std::string 	    material = "PLA";
+        bool                is_soluble = false;
         int  			    temperature = 0;
         int  			    first_layer_temperature = 0;
         float               loading_speed = 0.f;