Bug#12713 "Error in a stored function called from a SELECT doesn't

cause ROLLBACK of statement", part 1. Review fixes.

Do not send OK/EOF packets to the client until we reached the end of 
the current statement.
This is a consolidation, to keep the functionality that is shared by all 
SQL statements in one place in the server.
Currently this functionality includes:
- close_thread_tables()
- log_slow_statement().

After this patch and the subsequent patch for Bug#12713, it shall also include:
- ha_autocommit_or_rollback()
- net_end_statement()
- query_cache_end_of_result().

In future it may also include:
- mysql_reset_thd_for_next_command().

sql/sql_derived.cc

@@ -147,8 +147,9 @@ exit:
     /* Hide "Unknown column" or "Unknown function" error */
     if (orig_table_list->view)
     {
-      if (thd->net.last_errno == ER_BAD_FIELD_ERROR ||
-          thd->net.last_errno == ER_SP_DOES_NOT_EXIST)
+      if (thd->is_error() &&
+          (thd->main_da.sql_errno() == ER_BAD_FIELD_ERROR ||
+          thd->main_da.sql_errno() == ER_SP_DOES_NOT_EXIST))
       {
         thd->clear_error();
         my_error(ER_VIEW_INVALID, MYF(0), orig_table_list->db,