curseofwar-sdl: set mainProgram

pkgs/games/curseofwar/default.nix

@@ -32,6 +32,7 @@ stdenv.mkDerivation (finalAttrs: {
     description = "Fast-paced action strategy game";
     homepage = "https://a-nikolaev.github.io/curseofwar/";
     license = licenses.gpl3;
+    mainProgram = if SDL != null then "curseofwar-sdl" else "curseofwar";
     maintainers = with maintainers; [ fgaz ];
     platforms = platforms.all;
   };