OSV-2021-508 Segv on unknown address in Sass::CompoundSelector::resolve_parent_refs

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=31832 Crash type: Segv on unknown address Crash state: Sass::CompoundSelector::resolveparentrefs Sass::ComplexSelector::resolveparentrefs Sass::SelectorList::resolveparentrefs...