SPE-1739: Fixed calculation of gcode preview sequential slider endpoints

(cherry picked from commit 578921257d14e2c07611dfbb89cda5f9dc776e0c)

src/libslic3r/GCode.cpp

@@ -1609,6 +1609,7 @@ namespace DoExport {
         silent_time_estimator_enabled = (config.gcode_flavor == gcfMarlinLegacy || config.gcode_flavor == gcfMarlinFirmware)
                                         && config.silent_mode;
         processor.reset();
+        processor.initialize_result_moves();
         processor.apply_config(config);
         processor.enable_stealth_time_estimator(silent_time_estimator_enabled);
     }