Fixing explosive barrels prespawning skeletons

The AddBarrel function was not checking the type of the barrel when
generating the oVar2. This led to skeletons being pre-spawned in
explosive barrels; except that explosive barrels do not trigger the
spawn, resulting in unreachable monsters sitting at (0, 0) even after a
full clear.

While this does not affect functionality of regular Diablo gameplay, it
potentially affects modders who would like to use the nummonsters
global variable to check for full clears.

Source/objects.cpp

@@ -1100,7 +1100,7 @@ void AddBarrel(int i, int t)
 {
 	object[i]._oVar1 = 0;
 	object[i]._oRndSeed = GetRndSeed();
-	object[i]._oVar2 = random_(149, 10);
+	object[i]._oVar2 = (t == OBJ_BARRELEX) ? 0 : random_(149, 10);
 	object[i]._oVar3 = random_(149, 3);
 
 	if (object[i]._oVar2 >= 8)