bugfix: use_item scripts must return a value

src/scripts/eressea/embassy.lua

@@ -6,7 +6,9 @@ function use_seashell(u, amount)
     local msg = message("msg_event")
     msg:set_string("string", tostring(u) .. " erzählt den Bewohnern von " .. r.name .. " von Muschelplateau, das seine Partei vor " .. turns .. " Wochen besucht hat." )
     msg:send_region(u.region)
+    return 0
   end
+  return -4
 end
 
 function update_embassies()

src/scripts/eressea/xmas2004.lua

@@ -4,7 +4,9 @@ function use_snomwan(u, amount)
     u.race = "snowman"
     u.number = amount
     u:add_item("snowman", -amount)
+    return 0
   end
+  return -4
 end
 
 function xmas2004()

src/scripts/eressea/xmas2005.lua

@@ -1,7 +1,7 @@
-function usepotion_message(u, type)
+function usepotion_message(u, potion)
   msg = message("usepotion")
   msg:set_unit("unit", u)
-  msg:set_resource("potion", type)
+  msg:set_resource("potion", potion)
   return msg
 end
 
@@ -11,6 +11,8 @@ function use_stardust(u, amount)
   u.region:set_resource("peasant", p)
   local msg = usepotion_message(u, "stardust")
   msg:send_region(u.region)
+  u:add_item("stardust", -amount)
+  return 0
 end
 
 function xmas2005()