MDEV-35342 Server crashes when creating index on a rocksdb table

Debug assertion, added with MDEV-34880, did not take into account
that MyRocks sometimes uses hidden indexes that SQL layer isn't
aware of. This commit adds a proper handling for such cases

Author: Olernov

sql/handler.cc

@@ -3761,8 +3761,11 @@ int handler::ha_index_init(uint idx, bool sorted)
     end_range= NULL;
     /*
       Do not allow reads from UNIQUE HASH indexes.
+      (1) MyRocks sometimes uses hidden indexes that SQL layer isn't aware of,
+          skip the check for such cases
     */
-    DBUG_ASSERT(!(table->key_info[active_index].flags & HA_UNIQUE_HASH));
+    DBUG_ASSERT(active_index >= table->s->keys ||  // (1)
+                !(table->key_info[active_index].flags & HA_UNIQUE_HASH));
   }
 
   DBUG_RETURN(result);