Inform client if he doesn't have assets2.pk3 or assets5.pk3 when needed for joining a server

[ghost]

As of my experience, the client crashes if you try to join a 1.03 or 1.04 server and don't have assets2.pk3 or assets5.pk3 in your base folder. This could happen to people who use the standalone executable in their 1.02 folder. Instead of crashing, drop to main menu and inform the client that he needs these files?

[ouned]

jk2mv assumes 1.04 assets not just to play on 1.04 / 1.03 servers. e.g. the menu code depends on a patched version of jk2.
so jk2mv doesn't really make sense without those assets.