fix unicode awareness in mtmenu popups

mtmenu/mtmenu.lua

@@ -1,3 +1,4 @@
+local unicode = require "unicode"
 local event = require "event"
 local mtmenu = {}
 local mx, my
@@ -61,7 +62,7 @@ end
 
 function mtmenu.popup(str,title,state)
  local mx, my = mtmenu.getScreenSize()
- local len = (unicode or {}).len or string.len
+ local len = (unicode or {}).wlen or string.len
  if title then
   title=string.format("[%s]",title or "")
  else