Sporadic crashes on AES-CTR

[powersmc]

On three instances, I encountered bugs where the parser would crash (SEGFAULT) when attempting to process an AES-CTR vector. That being said, based on my investigation I don't think the issue was unique to AES-CTR. I believe the core issue resides here:

https://github.com/smuellerDD/acvpparser/blob/master/parser/read_json.c#L506

This code uses mmap to access the file contents as a buffer, and then subsequent code passes the buffer to string functions like strlen (https://github.com/smuellerDD/acvpparser/blob/master/parser/json-c/json_tokener.c#L260), which can end up accessing past the end of the buffer, as mmap doesn't guarantee a NULL terminator at the end of the buffer.

I was able to fix this locally by just switching from mmap to malloc, and adding in a NULL terminator myself. I can create a PR if desired, but I wasn't sure if that's the approach you wanted to take to fix this issue, or if you had something else in mind.