Fix crash when enabling in-game AA

[niligulmohar]

This change fixes a crash that could occur when enabling AA in the in-game menu.

In-game AA still does not work with DSfix though, and should be disabled.

[prototype99]

on my fork this fix does not break the game even with in game aa on, however it does reduce the game to a small square; presumably the original resolution of the game, the only things rendering correctly being the user interface