Fix SidedInvWrapper accessing wrong slots for setStackInSlot. (#2797)

Fix DoubleChestItemHandler not implementing IItemHandlerModifiable

src/main/java/net/minecraftforge/items/VanillaDoubleChestItemHandler.java

@@ -12,7 +12,7 @@ import java.lang.ref.WeakReference;
 
 import com.google.common.base.Objects;
 
-public class VanillaDoubleChestItemHandler extends WeakReference<TileEntityChest> implements IItemHandler
+public class VanillaDoubleChestItemHandler extends WeakReference<TileEntityChest> implements IItemHandlerModifiable
 {
     // Dummy cache value to signify that we have checked and definitely found no adjacent chests
     public static final VanillaDoubleChestItemHandler NO_ADJACENT_CHESTS_INSTANCE = new VanillaDoubleChestItemHandler(null, null, false);
@@ -91,6 +91,22 @@ public class VanillaDoubleChestItemHandler extends WeakReference<TileEntityChest
         return chest != null ? chest.getStackInSlot(targetSlot) : null;
     }
 
+    @Override
+    public void setStackInSlot(int slot, ItemStack stack)
+    {
+        boolean accessingUpperChest = slot < 27;
+        int targetSlot = accessingUpperChest ? slot : slot - 27;
+        TileEntityChest chest = getChest(accessingUpperChest);
+        if (chest != null)
+        {
+            IItemHandler singleHandler = chest.getSingleChestHandler();
+            if (singleHandler instanceof IItemHandlerModifiable)
+            {
+                ((IItemHandlerModifiable) singleHandler).setStackInSlot(targetSlot, stack);
+            }
+        }
+    }
+
     @Override
     public ItemStack insertItem(int slot, ItemStack stack, boolean simulate)
     {

src/main/java/net/minecraftforge/items/wrapper/SidedInvWrapper.java

@@ -144,7 +144,10 @@ public class SidedInvWrapper implements IItemHandlerModifiable
     @Override
     public void setStackInSlot(int slot, ItemStack stack)
     {
-        inv.setInventorySlotContents(slot, stack);
+        int slot1 = getSlot(inv, slot, side);
+
+        if (slot1 != -1)
+            inv.setInventorySlotContents(slot1, stack);
     }
 
     @Override