Fix redrawing of Undead 'done' clues after a resize.

Fix redrawing of Undead 'done' clues after a resize.

The is_hint_stale() function has the side effect of copying a path
hint's new colour-relevant information into the game_drawstate, where
draw_path_hint will then use it. But it returns TRUE early in some
situations, notably !ds->started, which can happen after the actual
game start if the window is resized and a fresh drawstate is created.

This patch, thanks to Chris Boyle, fixes it by eliminating the early
returns from is_hint_stale - the return value is unchanged, but now
the side effects happen reliably.