consider entire layout for gc

this fixes an issue where in some situations tiles would get erroneously
garbage collected and then immediately recreated, forming an infinite
loop and leading to 100% cpu load

main.ml

@@ -1216,7 +1216,7 @@ let act cmds =
           puttileopaque l col row gen cs angle opaque size t;
           S.memused := !S.memused + size;
           !S.uioh#infochanged Memused;
-          gctilesnotinlayout !S.layout;
+          gctilesnotinlayout layout;
           Queue.push ((l.pageno, gen, cs, angle, l.pagew, l.pageh, col, row),
                       opaque, size) S.tilelru;