Fix avrorouter memory leaks

The loading of the JSON schemas leaked memory as functions that increment
the reference count were used.

server/modules/routing/avrorouter/avro.c

@@ -414,6 +414,7 @@ createInstance(SERVICE *service, char **options)
     inst->gtid.seq = 0;
     inst->gtid.server_id = 0;
     inst->gtid.timestamp = 0;
+    memset(&inst->active_maps, 0, sizeof(inst->active_maps));
     bool err = false;
 
     if (param)