FIX: crush when slicer multi-color model

the root cause is a mismatch between the dimensions of flush matrix and the number of extruders

Change-Id: I3a4ca706cb24d9e5d33969b9e6f5b288e71bb8f2
(cherry picked from commit 7399037eaacdfd7d8407667a2e5a097757265254)

src/libslic3r/PresetBundle.cpp

@@ -2069,6 +2069,7 @@ void PresetBundle::load_config_file_config(const std::string &name_or_path, bool
     }
 
 	this->update_compatible(PresetSelectCompatibleType::Never);
+    this->update_multi_material_filament_presets();
 
     //BBS
     //const std::string &physical_printer = config.option<ConfigOptionString>("physical_printer_settings_id", true)->value;