message: Check return value from bson iter init
diff: @@ -622,7 +622,9 @@ core& core::open_array() {
  core& core::concatenate(const bsoncxx::document::view& view) {
  if (_impl->is_array()) {
  bson_iter_t iter;
  - bson_iter_init_from_data(&iter, view.data(), view.length());
  + if (!bson_iter_init_from_data(&iter, view.data(), view.length())) {
  + throw bsoncxx::exception{error_code::k_cannot_append_document};
  + }
  while (bson_iter_next(&iter)) {
  stdx::string_view key = _impl->next_key();
  