Show message 'no path' and exit if no path to reach the destination

[mdtareque]

Hi, I find pathFinding.js example playground very useful. It's robust and informative.

A suggestion, it would be good if a message is display and execution is stopped if there is no way to reach the destination. Currently, I see grid is searched infinitely to find a path to a blocked destination cell.

[stakira]

Path finding algorithms are not able to know target is unreachable before entire map is searched. This has to be handled with other strategy, i.e., out of scope of PathFinding.js.