Add defragmenting card piles to make dropping cards on a pile

to work in all situations.

init.lua

@@ -203,6 +203,41 @@ local function lighten_pile(pos)
    minetest.set_node(pos,node)
 end
 
+local function defragment_pile(pos)
+   local meta=minetest.get_meta(pos)
+   local pile_inv=meta:get_inventory()
+   local s=pile_inv:get_size("main")
+   local search_start=s-1
+   for i=s,1,-1 do
+      minetest.log("defrag:"..i)
+      local stack=pile_inv:get_stack("main",i)
+      if stack:is_empty() then
+	 for j=search_start,1,-1 do
+	    local st=pile_inv:get_stack("main",j)
+	    if st:is_empty() then
+	       minetest.log("defrag: empty stack i="..i.." j="..j)
+	    else
+	       pile_inv:set_stack("main",i,st)
+	       pile_inv:set_stack("main",j,ItemStack())
+	       minetest.log("defrag:move"..j.."->"..i)
+	       search_start=j-1
+	       if search_start==0 then
+		  minetest.log("defrag:exit at i="..i)
+		  return
+	       end
+	       break
+	    end
+	    if j==1 then
+	       minetest.log("defrag:exit at j=1")
+	       return
+	    end
+	 end
+      elseif search_start > i-1 then
+	 search_start=i-1
+      end
+   end
+end
+
 local function put_all_to_pile(pos,formname,fields,sender)
    local player_inv=minetest.get_inventory({type="player", name=sender:get_player_name()})
    local meta=minetest.get_meta(pos)
@@ -227,6 +262,8 @@ local function put_all_to_pile(pos,formname,fields,sender)
    end
    if pile_peek_first(pile_inv) == nil then
       darken_pile(pos)
+   else
+      defragment_pile(pos)
    end
 end
 
@@ -244,6 +281,8 @@ local function draw_one_card(pos,formname,fields,sender)
 	 player_inv:add_item("main",stack)
 	 if pile_peek_first(pile_inv) == nil then
 	    darken_pile(pos)
+	 else
+	    defragment_pile(pos)
 	 end
 	 return true
       end
@@ -268,6 +307,7 @@ local function shuffle_pile(pos,formname,fields,sender)
       for i=1,s,1 do
 	 pile_inv:set_stack("main",i,newpos[i])
       end
+      defragment_pile(pos)
 end
 
 local function convert_pile(pos,nodename)
@@ -288,6 +328,7 @@ local function convert_pile(pos,nodename)
       local stack=ItemStack(cards[i])
       newinv:set_stack("main",i,stack)
    end
+   defragment_pile(pos)
 end
 
 local function draw_card(pos,formname,fields,sender)