Don't use RS274NGC_STARTUP_CODE when updating the preview

This fixes issue #2753

Author: Sigma1912

src/emc/rs274ngc/gcodemodule.cc

@@ -777,11 +777,7 @@ static PyObject *parse_file(PyObject *self, PyObject *args) {
         if(!RESULT_OK) goto out_error;
         result = pinterp->execute();
     }
-    if(initcode && RESULT_OK) {
-        result = pinterp->read(initcode);
-        if(!RESULT_OK) goto out_error;
-        result = pinterp->execute();
-    }
+
     while(!interp_error && RESULT_OK) {
         error_line_offset = 1;
         result = pinterp->read();