libplugin: fix jsonrpc_set_datastore_binary/jsonrpc_set_datastore_string with NULL cb.

This should complete the command, otherwise we get an assertion on
line 1090.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Author: rustyrussell

plugins/libplugin.c

@@ -929,7 +929,7 @@ struct command_result *jsonrpc_set_datastore_(struct command *cmd,
 	struct out_req *req;
 
 	if (!cb)
-		cb = ignore_cb;
+		cb = ignore_and_complete;
 	if (!errcb)
 		errcb = plugin_broken_cb;