More itemstacks caching

Micro optimization on molecular assemblers

src/main/java/appeng/tile/inventory/AppEngInternalInventory.java

@@ -77,6 +77,10 @@ public class AppEngInternalInventory extends ItemStackHandler implements Iterabl
 	@Override
 	public void setStackInSlot( int slot, @Nonnull ItemStack stack )
 	{
+		if( stack == this.getStackInSlot( slot ) )
+		{
+			return;
+		}
 		this.previousStack = this.getStackInSlot( slot ).copy();
 		super.setStackInSlot( slot, stack );
 	}