Optimization is_string struct
优化is_string对象

Signed-off-by: Wanpeng Song <swpustc@mail.ustc.edu.cn>
Update dumpImageSize version to 1.1.6.12
更新dumpImageSize版本到1.1.6.12

Signed-off-by: Wanpeng Song <swpustc@mail.ustc.edu.cn>