fix realloc crashing on linux

[markus-k]

Hi!

thank you for providing this utility, it helped a lot!

But I noticed it instantly crashes on Linux since the pointer passed to realloc was not initially allocated using malloc or calloc. So here's a quick pull request in case anyone ever needs this again.

[mindcruzer]

Hey Markus, I took a look at this I am not sure why it would be crashing for you. If you check the realloc spec it’s analogous to a call to malloc when passed a NULL pointer.

[markus-k]

Huh you are right, not sure how I came to that conclusion. I had a look at it again, and the actual problem was just a missing memset on the memory allocated in read_bkn. This caused the pointer and size in read_bkn_method to be just random bytes, which caused the crash. Will fix the PR