OSV-2021-1526 Global-buffer-overflow in fr_unix_time_from_tm

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=40600 Crash type: Global-buffer-overflow READ 2 Crash state: frunixtimefromtm frunixtimefromstr frvalueboxfromsubstr...