Revert "bookstatus(fix): reset self.stats on init"

This reverts commit be8ceb84b4.

frontend/ui/widget/bookstatuswidget.lua

@@ -50,15 +50,15 @@ local BookStatusWidget = InputContainer:new{
         status = "",
         modified = "",
     },
-    stats = nil
+    stats = {
-}
-
-function BookStatusWidget:init()
-    self.stats = {
         total_time_in_sec = 0,
         performance_in_pages = {},
-        pages = self.document:getPageCount(),
+        pages = 0,
     }
+}
+
+function BookStatusWidget:init()
+    self.stats.pages = self.document:getPageCount()
     self:getStatisticsSettings()
     if self.settings then
         self.summary = self.settings:readSetting("summary")