Mod switching is broken if mod being switched to isn't installed already

[Aciz]

1. Start the game with any mod
2. Connect to a server running mod that you don't have installed (fs_game folder contains no mod binaries)
3. User interface is version 0, expected 4 error pops up.

Works on Linux, but not on Windows (macOS unknown).

[Aciz]

This is actually broken on Linux too, so I presume all platforms are affected.