ASAN error when strlen(db) < 6

sql/table.cc

@@ -324,7 +324,8 @@ TABLE_SHARE *alloc_table_share(const char *db, const char *table_name,
     share->can_do_row_logging= 1;
     if (share->table_category == TABLE_CATEGORY_LOG)
       share->no_replicate= 1;
-    if (my_strnncoll(table_alias_charset, (uchar*) db, 6,
+    if (key_length > 6 &&
+        my_strnncoll(table_alias_charset, (const uchar*) key, 6,
                      (const uchar*) "mysql", 6) == 0)
       share->not_usable_by_query_cache= 1;