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_partition.cc

@@ -2068,6 +2068,7 @@ char *generate_partition_syntax(partition_info *part_info,
     default:
       DBUG_ASSERT(0);
       /* We really shouldn't get here, no use in continuing from here */
+      my_error(ER_OUT_OF_RESOURCES, MYF(0));
       current_thd->fatal_error();
       DBUG_RETURN(NULL);
   }