Fix mantis 2753: save csg just before mission starts
read loadout indexes into int instead of uint & ensure -1 is not used as array index
initialise Player_loadout struct during FSO start

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@9657 387891d4-d844-0410-90c0-e4c51a9137d3