Fix pointer addition with NULL pointer

[7YZ7]

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为什么提交这份PR (why to submit this PR)

在第393行和第401行代码中，将 NULL 指针（(char )0）与另一个指针或整数相加。当与空指针进行算术操作时，结果是未定义的。 你的解决方案是什么 (what is your solution) 将 arg 与 (char )0 指针相减，可以改为直接将 arg 强制转换为 int 类型。同样，将 count 与 (char )0 相加也可以改为将 count 强制转换为 void 类型。这里使用了 intptr_t 类型，它是一个整数类型，可以保证在转换为指针类型时不会丢失数据。

在什么测试环境下测试通过 (what is the test environment) all

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[tencent-adm]

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[Supowang1989]

@Yangyuanxin 帮忙review下这个修改