Bug#43201: Post-fix. Set thread stack address at the start of each query.

Reason: implementation of send/reap in mysqltest uses the same "embedded" connection in a thread different from current, so thread stack has to change when connection is used in different  OS thread..

libmysqld/lib_sql.cc

@@ -118,6 +118,7 @@ emb_advanced_command(MYSQL *mysql, enum enum_server_command command,
   net_clear_error(net);
   thd->current_stmt= stmt;
 
+  thd->thread_stack= (char*) &thd;
   thd->store_globals();				// Fix if more than one connect
   /* 
      We have to call free_old_query before we start to fill mysql->fields