dont draw decals on black abyss tile

[Cokemonkey11]

• custom tile needed?
• maybe just change projectile for grenadier?

[Cokemonkey11]

Changed grenadier projectile a long time ago and that's good enough

[Cokemonkey11]

False - never changed the projectile.

Abilities.mortarMissile is the offender.

[Cokemonkey11]

fix a cosmetic bug related to mortar team missile art. Closes #57

→ <<cset 215fa9db2bc8>>