PS-9537 fix: Existing connection cannot be reused to run multiple queries in Command Services

https://perconadev.atlassian.net/browse/PS-9537

Fixed problem with re-using the same connection created via
'mysql_command_factory->init()' / 'mysql_command_factory->connect()'
in multiple calls to' mysql_command_query->query()'.

The problem seems to be a regression introduced by upstream in their fix for
Bug #34323788
"ASAN memory leaks reported by test_mysql_command_services_component.test"
(commit mysql/mysql-server@5dc1a14).

Inside 'csi_advanced_command()' 'mcs_extn->consumer_srv_data' when is
not nullptr cannot be simply re-used as its `mcs_extn->data` member
has already been set to nullptr by `std::exchange()` inside `csi_read_rows()`.

Fixed by calling 'factory_srv->end()' and 'factory_srv->start()' in this case.

Author: percona-ysorokin

sql/server_component/mysql_command_backend.cc

@@ -306,10 +306,13 @@ bool csi_advanced_command(MYSQL *mysql, enum enum_server_command command,
   }
 
   mysql_handle.mysql = mysql;
-  if (mcs_extn->consumer_srv_data != nullptr)
-    srv_ctx_h = reinterpret_cast<SRV_CTX_H>(mcs_extn->consumer_srv_data);
-  else if (((class mysql_command_consumer_refs *)(command_consumer_srv))
-               ->factory_srv->start(&srv_ctx_h, (MYSQL_H *)&mysql_handle)) {
+  if (mcs_extn->consumer_srv_data != nullptr) {
+    ((class mysql_command_consumer_refs *)(command_consumer_srv))
+        ->factory_srv->end(
+            reinterpret_cast<SRV_CTX_H>(mcs_extn->consumer_srv_data));
+  }
+  if (((class mysql_command_consumer_refs *)(command_consumer_srv))
+          ->factory_srv->start(&srv_ctx_h, (MYSQL_H *)&mysql_handle)) {
     sprintf(*err_msg, "Could not create %s service",
             "mysql_text_consumer_factory_v1");
     goto error;