Add functionality in IItemHandler to test if a slot can accept an item (#5033)

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

@@ -164,6 +164,12 @@ public class ItemStackHandler implements IItemHandler, IItemHandlerModifiable, I
         return Math.min(getSlotLimit(slot), stack.getMaxStackSize());
     }
 
+    @Override
+    public boolean isItemValid(int slot, @Nonnull ItemStack stack)
+    {
+        return true;
+    }
+
     @Override
     public NBTTagCompound serializeNBT()
     {