save game more frequently

save game when mission screen is setPlayMissionGui is called which is reasonable enough

marble/client/init.cs

@@ -237,6 +237,8 @@ function findNamedFile(%file, %ext)
 
 function setPlayMissionGui()
 {
+   // save game too
+   export("$pref::*", "./prefs.cs", False);
    Canvas.setContent(playMissionGui);
 }