Update screensaver.lua (#5123)

Change to use Math.round()

frontend/ui/screensaver.lua

@@ -7,6 +7,7 @@ local DocSettings = require("docsettings")
 local DocumentRegistry = require("document/documentregistry")
 local InfoMessage = require("ui/widget/infomessage")
 local ImageWidget = require("ui/widget/imagewidget")
+local Math = require("optmath")
 local ScreenSaverWidget = require("ui/widget/screensaverwidget")
 local UIManager = require("ui/uimanager")
 local lfs = require("libs/libkoreader-lfs")
@@ -402,7 +403,7 @@ function Screensaver:expandSpecial(message, fallback)
         local totalpages = doc:getPageCount()
         ret = string.gsub(ret, "%%t", totalpages)
 
-        local percent = math.floor(((currentpage * 100) / totalpages) + 0.5)
+        local percent = Math.round((currentpage * 100) / totalpages)
         ret = string.gsub(ret, "%%p", percent)
 
         local props = doc:getProps()