Fixed RasPi builds of unit tests.

On RasPi with gcc 4.8.2, the asserts wouldn't compile when tests were enabled.
Enforced the assumption that ASSERT code is generated only in Debug builds.

src/Entities/Entity.cpp

@@ -741,7 +741,9 @@ bool cEntity::ArmorCoversAgainst(eDamageType a_DamageType)
 		}
 	}
 	ASSERT(!"Invalid damage type!");
-	return false;
+	#ifndef __clang__
+		return false;
+	#endif
 }