fix game crashing when showing a too large tooltip

previously the game would go into an infinite loop at
https://github.com/wesnoth/wesnoth/blob/1.14.4/src/gui/widgets/window.cpp#L1046
when a tooltip doesn't fit on screen, this could in particular happen in
the mp lobby when hovering over the 'i' of a game that uses a ridiculous
amount of modifications.

I currently don't see any case where the game is actually able to 'fix'
a bad height that was reported from reevaluate_best_size. so i just
disable reevaluate_best_size for floating tooltips.

If there exists such a case, an alternative fix could be to change the
reevaluate loop in window::layout to also stop when a new iteration
returned the same size as the previous iteration.

data/gui/window/tooltip_floating.cfg

@@ -97,7 +97,7 @@ def set_w(r, w, s)
 def reevaluate_best_size(w, s)
 (
 [
-	w.y > s.y,
+	0,
 #
 	debug_print('window ', w),
 	debug_print('screen ', s)