fix: stop self.dimen polution for inputcontainers

Without this fix, self.dimen is shared among all inputcontainers
intances, which breaks some of the UI rendering. All widget should
set/initialize their own self.dimen in self:init() method.

frontend/apps/reader/modules/readerconfig.lua

@@ -13,6 +13,7 @@ local ReaderConfig = InputContainer:new{
 }
 
 function ReaderConfig:init()
+    if not self.dimen then self.dimen = Geom:new{} end
     if Device:hasKeyboard() then
         self.key_events = {
             ShowConfigMenu = { { "AA" }, doc = "show config dialog" },