Bug#53046 dict_update_statistics_low can still be run concurrently

on same table

Followup to vasil.dimov@oracle.com-20100428102033-dt3caf531rs3lidr :

Add more asserions, which I forgot.

storage/innodb_plugin/dict/dict0dict.c

@@ -274,6 +274,11 @@ dict_index_stat_mutex_exit(
 /*=======================*/
 	const dict_index_t*	index)	/*!< in: index */
 {
+	ut_ad(index != NULL);
+	ut_ad(index->magic_n == DICT_INDEX_MAGIC_N);
+	ut_ad(index->cached);
+	ut_ad(!index->to_be_dropped);
+
 	mutex_exit(GET_INDEX_STAT_MUTEX(index));
 }