Fixes overflow in fork_and_trace()
Fixes overflow in fork_and_trace()

Introduces by 7f99bcc87ddaf47aa06710fcc4f1c22c8db47706, it's actually
been here for a while.

ViDA-NYU/reprozip,JosuaKrause/reprozip,ViDA-NYU/reprozip,JosuaKrause/reprozip,ViDA-NYU/reprozip,ViDA-NYU/reprozip,JosuaKrause/reprozip,JosuaKrause/reprozip,ViDA-NYU/reprozip