check for NULL ptr in _mesa_print_parameter_list()

src/mesa/shader/prog_print.c

@@ -753,6 +753,9 @@ _mesa_print_parameter_list(const struct gl_program_parameter_list *list)
    const gl_prog_print_mode mode = PROG_PRINT_DEBUG;
    GLuint i;
 
+   if (!list)
+      return;
+
    _mesa_printf("param list %p\n", (void *) list);
    for (i = 0; i < list->NumParameters; i++){
       struct gl_program_parameter *param = list->Parameters + i;