fix several potential vulnerabilities

[YangY-Xiao]

fixing oob, null pointer deference

[YangY-Xiao]

How about the last two commits?

[YangY-Xiao]

so, line 495 in kwajd.c is not necessary, isn't it? https://github.com/kyz/libmspack/blob/master/libmspack/mspack/kwajd.c#L495

[kyz]

Thanks very much for looking for potential vulnerabilities. What's in this patch is already fixed, but please do share any other vulnerabilities you find in future.

[kyz]

so, line 495 in kwajd.c is not necessary, isn't it? https://github.com/kyz/libmspack/blob/master/libmspack/mspack/kwajd.c#L495

Yes, that's correct. It could just be if (lzh) lzh->sys->free(lzh);

[YangY-Xiao]

so, line 495 in kwajd.c is not necessary, isn't it? https://github.com/kyz/libmspack/blob/master/libmspack/mspack/kwajd.c#L495

Yes, that's correct. It could just be if (lzh) lzh->sys->free(lzh);

Gotcha. So, for coordinating the code should be changed.