title: A* Pathfinding - closest to unwalkable destination
body: <p>I already have an A* Implementation that works.  The problem is that if you pick a destination that is unwalkable, no path is returned.  I want to be able to get the 'closest' I can get.</p>
  
  <p>The preferable option would be completely dynamic (not just checking the 8 tiles around the destination to try to find one).  That way, even if they click an unwalkable tile surrounded by a huge square of unwalkable tiles, it will still get as close as it can.</p>