Revert to default saber if selected saber does not exist

[Firepal]

I noticed while working on a new saber (~~PR coming soon enough~~ Nevermind, bad git operation deleted the branch) that saving in a version of the game that contains a new saber THEN opening a version of the game without the new saber causes the game to try to select a saber that doesn't exist, and an out-of-bounds array access exception is thrown.

This PR adds code that checks if the selected saber exists, and if it doesn't, reverts to default saber.