Write unlock.vvv when pressing Alt+F4

Previously, the only way to guarantee that the game actually saved your
unlock.vvv after changing an option, was to ensure you pressed ACTION on
the "quit game" menu option.

This makes Alt+F4 graceful in that pressing it will also save
unlock.vvv, as it should. Now truly UN-graceful ways of exiting the
game, such as SIGSEGV, SIGABRT, or pkill -9 or pkill -15 will not save
unlock.vvv, as should be the case.

desktop_version/src/main.cpp

@@ -575,6 +575,7 @@ int main(int argc, char *argv[])
     //SDL_FreeSurface( gameScreen );
 
     //Quit SDL
+    game.savestats(map, graphics);
     NETWORK_shutdown();
     SDL_Quit();
     FILESYSTEM_deinit();