go/zodb/zeo: Load: Fix thinko when rejecting result

If xres fails to convert to tuple, we should error about xres, not res
which is always tuple(nil).

go/zodb/storage/zeo/zeo.go

@@ -92,7 +92,7 @@ func (z *zeo) Load(ctx context.Context, xid zodb.Xid) (buf *mem.Buf, serial zodb
 	// (data, serial, next_serial | None)
 	res, ok := enc.asTuple(xres)
 	if !ok || len(res) != 3 {
-		return nil, 0, rpc.ereplyf("got %#v; expect 3-tuple", res)
+		return nil, 0, rpc.ereplyf("got %#v; expect 3-tuple", xres)
 	}
 
 	data, ok1 := enc.asBytes(res[0])