Misc improvements for CombinedContainer

src/main/kotlin/ru/dbotthepony/mc/otm/container/CombinedContainer.kt

@@ -93,27 +93,7 @@ class CombinedContainer(containers: Stream<Pair<IEnhancedContainer, Iterable<Int
 	}
 
 	override fun isEmpty(): Boolean {
-		if (fullCoverage.isNotEmpty())
+		return fullCoverage.all { it.isEmpty } && notFullCoverage.values.all { it.all { it.isEmpty } }
-			for (container in fullCoverage)
-				if (!container.isEmpty)
-					return false
-
-		if (notFullCoverage.isNotEmpty())
-			for (slots in notFullCoverage.values)
-				for (slot in slots)
-					if (!slot.isEmpty)
-						return false
-
-		return true
-	}
-
-	override fun getItem(slot: Int): ItemStack {
-		// do not violate contract of getItem not throwing exceptions when index is invalid
-		return slots.getOrNull(slot)?.item ?: ItemStack.EMPTY
-	}
-
-	override fun setItem(slot: Int, itemStack: ItemStack) {
-		slots.getOrNull(slot)?.item = itemStack
 	}
 
 	override fun setChanged() {
@@ -123,11 +103,7 @@ class CombinedContainer(containers: Stream<Pair<IEnhancedContainer, Iterable<Int
 	}
 
 	override fun stillValid(player: Player): Boolean {
-		for (container in containers)
+		return containers.all { it.stillValid(player) }
-			if (!container.stillValid(player))
-				return false
-
-		return true
 	}
 
 	override fun iterator(): Iterator<ItemStack> {