ReaderRolling: update footer when TOC is updated (#3950)

Footer item "pages left in chapter" was wrong when changing font
sizes or some other layout option (the footer was drown before
this happen, and not after, until we later change page).
Seems to also fix possible wrong ticks position in that case
(may be only when cache is used/re-used, for some not really
obvious reason)

frontend/apps/reader/modules/readerrolling.lua

@@ -563,6 +563,7 @@ function ReaderRolling:updatePos()
         self.old_doc_height = new_height
         self.old_page = new_page
         self.ui:handleEvent(Event:new("UpdateToc"))
+        self.view.footer:updateFooter()
     end
     UIManager:setDirty(self.view.dialog, "partial")
 end