Fix loading saved game prior to commit 7e21048 crash.

Commit 7e21048 introduced a change in the save game files strutcure.
This makes the game crash whenever you load saved games created with a prior version of the code.
This commit tends to fix this issue.
However, save game files created between commit 7e21048 and the current one will not load correclty.
Unless the user change the saved game's saveVersion number in game.details.