fix incompatibility with mining drones

[wietlol]

fix issue where mods that created entities that don't have enraged versions, would crash the game when those entities would fall below half health

it now verifies that the enraged version of the entity actually exists

[MrNiknoc]

While this may be a solution I use in the future, I fixed this incompatibility by making Mining Drones an optional dependency of Angry Biters. This means that the enraged versions of the drones should now exist, and this crash should be fixed.