message: reflection: check for valid union enum value during object verification
  ... to avoid assertion failure or invalid access due to invalid vector index
diff: @@ -656,6 +656,7 @@ bool VerifyObject(flatbuffers::Verifier &v, const reflection::Schema &schema,
  if (utype != 0) {
  // Means we have this union field present
  auto fb_enum = schema.enums()->Get(field_def->type()->index());
  + if (utype >= fb_enum->values()->size()) return false;
  auto child_obj = fb_enum->values()->Get(utype)->object();
  if (!VerifyObject(v, schema, *child_obj,
  flatbuffers::GetFieldT(*table, *field_def),
  