Correctly modify player sample with hidden player counts.

At the moment the setPlayers() method will throw a NullPointerException
if the player count has been hidden. This will correctly reset the
player counts before setting the player list and return null in the
getter instead of throwing an exception.
Return an empty list instead of null when getting the player sample.
Correctly handle player samples set to null.
Merge pull request #37 from Minecrell/patch-3

Correctly modify player sample with hidden player counts.