OSV-2022-412 Bad-cast to const upb_tabent' (aka 'const struct _upb_tabent')insert

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=47464 Crash type: Bad-cast Crash state: Bad-cast to const upbtabent' aka 'const struct upbtabent'insert upbstrtableinsert createfielddef...