Temporary fix for TAO

Summary: I'm investigating a TAO crash and while I'm not yet sure of the root cause, I know where it is crashing.  Add some checks in the code to prevent the crash from occurring to see if TAO can make progress while waiting for the root cause fix.

Differential Revision: D63038824

fbshipit-source-id: d01e733f152ccbf19f14055295d9a920e3a112ee

third-party/squangle/src/squangle/mysql_client/mysql_protocol/MysqlResult.cpp

@@ -16,20 +16,32 @@ namespace facebook::common::mysql_client::mysql_protocol {
 class MysqlRowMetadata;
 
 size_t MysqlResult::numFields() const {
+ // T202181457
+ if (!res_) {
+ return 0;
+ }
  auto ret = mysql_num_fields(res_.get());
  VLOG(4) << fmt::format(
  "mysql_num_fields({}) returned {}", (void*)res_.get(), ret);
  return ret;
 }
 
 MYSQL_FIELD* MysqlResult::fields() const {
+ // T202181457
+ if (!res_) {
+ return nullptr;
+ }
  auto ret = mysql_fetch_fields(res_.get());
  VLOG(4) << fmt::format(
  "mysql_fetch_fields({}) returned {}", (void*)res_.get(), (void*)ret);
  return ret;
 }
 
 size_t MysqlResult::numRows() const {
+ // T202181457
+ if (!res_) {
+ return 0;
+ }
  auto ret = mysql_num_rows(res_.get());
  VLOG(4) << fmt::format(
  "mysql_num_rows({}) returned {}", (void*)res_.get(), ret);
@@ -64,6 +76,8 @@ InternalResult::FetchRowRet MysqlRowFactory(
 } // namespace
 
 InternalResult::FetchRowRet SyncMysqlResult::fetchRow() {
+ // T202181457
+ CHECK(res_);
  auto mysqlRow = mysql_fetch_row(res_.get());
  VLOG(4) << fmt::format(
  "mysql_fetch_row({}) returned {}", (void*)res_.get(), (void*)mysqlRow);
@@ -74,6 +88,12 @@ InternalResult::FetchRowRet SyncMysqlResult::fetchRow() {
 InternalResult::FetchRowRet AsyncMysqlResult::fetchRow() {
  std::unique_ptr<InternalRow> row;
 
+ // T202181457
+ if (!res_) {
+ return std::make_pair(
+ MysqlConnection::toHandlerStatus(NET_ASYNC_ERROR), std::move(row));
+ }
+
  MYSQL_ROW mysqlRow;
  auto ret = mysql_fetch_row_nonblocking(res_.get(), &mysqlRow);
  VLOG(4) << fmt::format(