Lua Desintegrate remove walls

[mpa]

The desintegrate rune can be used to remove walls!!
How can you change this?
Here is the script:

local function doRemoveObject(cid, pos)
 pos.stackpos = 1
 local object = getThingfromPos(pos)
 if(object.uid > 65535 and isCreature(object.uid) == FALSE and isMovable(object.uid) == FALSE and object.actionid == 0 and getTilePzInfo(pos) == FALSE) then
  doRemoveItem(object.uid)
  doSendMagicEffect(pos, CONST_ME_BLOCKHIT)
  return LUA_NO_ERROR
 end
 doPlayerSendDefaultCancel(cid, RETURNVALUE_NOTPOSSIBLE)
 doSendMagicEffect(getPlayerPosition(cid), CONST_ME_POFF)
 return LUA_ERROR
end
function onCastSpell(cid, var)
 local pos = variantToPosition(var)
 if(pos.x ~= 0 and pos.y ~= 0 and pos.z ~= 0) then
  return doRemoveObject(cid, pos)
 end
 doPlayerSendDefaultCancel(cid, RETURNVALUE_NOTPOSSIBLE)
 doSendMagicEffect(getPlayerPosition(cid), CONST_ME_POFF)
 return LUA_ERROR
end