Items and blocks can't be put in an item frame with the off-hand

The bug

If you try put an item or a block in an item frame with the off-hand if you have nothing in you main hand, nothing happens.

Code analysis

Based on 1.11 decompiled using MCP 9.35 rc1

The problem is that the method net.minecraft.entity.item.EntityItemFrame.processInitialInteract(EntityPlayer, EnumHand) always returns true even if the no item was placed nor the item in the item frame was rotated. This makes the game skip the offhand. The check whether or not the world is a server world has to be removed as well because otherwise the client would always try to interact with both hands because it would always fail.

Fix

EntityItemFrame.java

public boolean processInitialInteract(EntityPlayer player, EnumHand hand)
    {
        ItemStack itemstack = player.getHeldItem(hand);

//      if (!this.world.isRemote)
//      {
            if (this.getDisplayedItem().isEmpty())
            {
                if (!itemstack.isEmpty())
                {
                    this.setDisplayedItem(itemstack);

                    if (!player.capabilities.isCreativeMode)
                    {
                        itemstack.shrink(1);
                    }

++                  return true;
                }
				
++		return false;
            }
            else
            {
                this.playSound(SoundEvents.ENTITY_ITEMFRAME_ROTATE_ITEM, 1.0F, 1.0F);
                this.setItemRotation(this.getRotation() + 1);
            }
//      }

        return true;
    }