[A17] Trading on world map gives spacey music

[Mehni]

What happens:
Any time you trade while on the world map, inappropriate "spacey" music is heard. This is for trading with bases and caravan encounters.

What you expected to happen.
I'd like some more appropriate (less jarring) music, or just no music.

Repro steps:
1. From trade caravan.
2. Trade while on world map, either with friendly faction base or friendly caravan encounter.
3. Listen to music.

[ison]

Fixed for A18, thanks.