Buying plots seems to be sometimes unstable

[verymilan]

Once we tried buying a church (as i remember) and this was the result:

ServerError: Lua: Runtime error from mod 'mg_villages' in callback on_playerReceiveFields(): Invalid position (expected table got nil).
stack traceback:
      [C]: in function 'get_meta'
      ...n/../games/minetest_game/mods/mg_villages/protection.lua:178: in function 'plotmarker_formspec'
      ...n/../games/minetest_game/mods/mg_villages/protection.lua:556: in function <...n/../games/minetest_game/mods/mg_villages/protection.lua:549>
      /bin/../builtin/game/register.lua:412: in function </home/minetest/t2minetest/bin/../builtin/game/register.lua:392>