for(c = sel->prev; c && !isvisible(c); c = c->prev);
if(!c) {
for(c = clients; c && c->next; c = c->next);
for(; c && !isvisible(c); c = c->prev);
}
for(c = sel->prev; c && !isvisible(c); c = c->prev);
if(!c) {
for(c = clients; c && c->next; c = c->next);
for(; c && !isvisible(c); c = c->prev);
}