OSV-2021-1216 Global-buffer-overflow in fr_is_base16_nstd

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=38283 Crash type: Global-buffer-overflow READ 1 Crash state: frisbase16nstd frbase16decodenstd frvalueboxfromstr...