OSV-2020-1453 UNKNOWN READ in RDKit::labelRecursivePatterns

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=24352 Crash type: UNKNOWN READ Crash state: RDKit::labelRecursivePatterns RDKit::SmartsToMol RDKit::ParseMarvinSmartsLine...