Enemies firing sound is muted if there's a wall between the player and the enemy

This is noticeable on E1M1 on the S.T.A.R. Trooper secret. It's hard to find out when they stopped shooting so you can peek and shoot at them.

**SFX Type:** Adlib
**OS:** Arch Linux
**Package:** bstone 1.2.13-1 (AUR)