Add player object check.

* Handle the case where a mob somehow "clicks" on a composter and we get
  an invalid player object passed.

mods/ITEMS/mcl_composters/init.lua

@@ -139,7 +139,7 @@ local function composter_add_item(pos, node, player, itemstack, pointed_thing)
 	-- handle filling the composter when rightclicked
 	-- as an on_rightclick handles, it returns an itemstack
 	--
-	if not player or player:get_player_control().sneak then
+	if not player or (player:get_player_control() and player:get_player_control().sneak) then
 		return itemstack
 	end
 	if not itemstack and itemstack:is_empty() then