Modules: associate a fake client to cluster message context callback.

Fixes #5354.

src/module.c

@@ -3938,6 +3938,8 @@ void moduleCallClusterReceivers(const char *sender_id, uint64_t module_id, uint8
         if (r->module_id == module_id) {
             RedisModuleCtx ctx = REDISMODULE_CTX_INIT;
             ctx.module = r->module;
+            ctx.client = moduleKeyspaceSubscribersClient;
+            selectDb(ctx.client, 0);
             r->callback(&ctx,sender_id,type,payload,len);
             moduleFreeContext(&ctx);
             return;