fix integer underflow in tile()

When clients don't fit, my or ty can exceed m->w.height, and since they
were unsigned, m->w.height - my wrapped around to huge heights, hanging
dwl. With signed ints the height can become negative instead, which
applybounds() raises to the minimum size.

Fixes: https://codeberg.org/dwl/dwl/issues/1254

dwl.c

@@ -3054,8 +3054,7 @@ tagmon(const Arg *arg)
 void
 tile(Monitor *m)
 {
-	unsigned int mw, my, ty;
-	int i, n = 0;
+	int i, n = 0, mw, my, ty;
 	Client *c;
 
 	wl_list_for_each(c, &clients, link)