Significantly reduce memory usage by cells

src/main/kotlin/ru/dbotthepony/kstarbound/client/world/ClientWorld.kt

@@ -55,19 +55,11 @@ class ClientWorld(
 	val renderRegionsY = size.y / renderRegionHeight
 
 	fun isValidRenderRegionX(value: Int): Boolean {
-		if (loopX) {
+		return loopX || value in 0 .. renderRegionsX
-			return true
-		} else {
-			return value in 0 .. renderRegionsX
-		}
 	}
 
 	fun isValidRenderRegionY(value: Int): Boolean {
-		if (loopY) {
+		return loopY || value in 0 .. renderRegionsY
-			return true
-		} else {
-			return value in 0 .. renderRegionsY
-		}
 	}
 
 	inner class RenderRegion(val x: Int, val y: Int) {

src/main/kotlin/ru/dbotthepony/kstarbound/world/api/AbstractLiquidState.kt

@@ -2,6 +2,7 @@ package ru.dbotthepony.kstarbound.world.api
 
 import ru.dbotthepony.kstarbound.Registries
 import ru.dbotthepony.kstarbound.defs.tile.LiquidDefinition
+import ru.dbotthepony.kstarbound.util.HashTableInterner
 import java.io.DataInputStream
 
 sealed class AbstractLiquidState {

src/main/kotlin/ru/dbotthepony/kstarbound/world/api/MutableCell.kt

@@ -29,7 +29,10 @@ data class MutableCell(
 	}
 
 	override fun immutable(): ImmutableCell {
-		return ImmutableCell(foreground.immutable(), background.immutable(), liquid.immutable(), dungeonId, biome, envBiome, isIndestructible)
+		val result = ImmutableCell(foreground.immutable(), background.immutable(), liquid.immutable(), dungeonId, biome, envBiome, isIndestructible)
+		if (result == NULL) return NULL
+		if (result == EMPTY) return EMPTY
+		return result
 	}
 
 	override fun mutable(): MutableCell {

src/main/kotlin/ru/dbotthepony/kstarbound/world/api/MutableLiquidState.kt

@@ -23,6 +23,8 @@ data class MutableLiquidState(
 	}
 
 	override fun immutable(): ImmutableLiquidState {
-		return ImmutableLiquidState(def, level, pressure, isInfinite)
+		val result = ImmutableLiquidState(def, level, pressure, isInfinite)
+		if (result == EMPTY) return EMPTY
+		return result
 	}
 }