Logic errors as reported by scan-build

Hello!

Scan-build reported 2 logic errors. Here is the report: https://rootkea.gitlab.io/ristretto/scan-build/

1. Array subscript is undefined
2. Dereference of undefined pointer value

And here is the .gitlab-ci.yml which generated above report: https://gitlab.com/rootkea/ristretto/-/blob/gitlab-scan-build/.gitlab-ci.yml

Thanks!