Add defensive check for null timeout manager in waitForActionable

Summary:
Adds a defensive check in MysqlOperationImpl::waitForActionable() to gracefully fail if getTimeoutManager() returns null. This can happen during client shutdown when AsyncConnection::~AsyncConnection() schedules a reset operation, but the EventBase is already being destroyed.

Without this check, the operation would crash with an assertion failure in AsyncTimeout::scheduleTimeout() when it tries to use a null timeoutManager_. With this fix, the operation fails gracefully with OperationResult::Failed instead of crashing.

Reviewed By: rban1

Differential Revision: D94744809

fbshipit-source-id: 7c9d067b22d1ca84ad4386aedf7f864dc10fff3d

Author: Jay Edgar

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

@@ -61,6 +61,13 @@ MysqlConnection* MysqlOperationImpl::getMysqlConnection() {
 void MysqlOperationImpl::waitForActionable() {
   DCHECK(isInEventBaseThread());
 
+  // Check if timeout manager is still valid (EventBase not shutting down)
+  // This can happen if an operation is scheduled during client shutdown
+  if (!getTimeoutManager()) {
+    completeOperation(OperationResult::Failed);
+    return;
+  }
+
   auto event_mask = getMysqlConnection()->getReadWriteState();
 
   if (hasOpElapsed(getTimeout())) {