Remember scroll mode in flipping mode

This is a follow-up workaround on #1439.

frontend/apps/reader/modules/readerpaging.lua

@@ -127,6 +127,7 @@ function ReaderPaging:onReadSettings(config)
         self.show_overlap_enable = DSHOWOVERLAP
     end
     self.flipping_zoom_mode = config:readSetting("flipping_zoom_mode") or "page"
+    self.flipping_scroll_mode = config:readSetting("flipping_scroll_mode") or false
 end
 
 function ReaderPaging:onSaveSettings()
@@ -135,6 +136,7 @@ function ReaderPaging:onSaveSettings()
     self.ui.doc_settings:saveSetting("percent_finished", self:getLastPercent())
     self.ui.doc_settings:saveSetting("show_overlap_enable", self.show_overlap_enable)
     self.ui.doc_settings:saveSetting("flipping_zoom_mode", self.flipping_zoom_mode)
+    self.ui.doc_settings:saveSetting("flipping_scroll_mode", self.flipping_scroll_mode)
 end
 
 function ReaderPaging:getLastProgress()
@@ -258,7 +260,7 @@ function ReaderPaging:enterFlippingMode()
     self.DGESDETECT_DISABLE_DOUBLE_TAP = DGESDETECT_DISABLE_DOUBLE_TAP
 
     self.view.document.configurable.text_wrap = 0
-    self.view.page_scroll = false
+    self.view.page_scroll = self.flipping_scroll_mode
     Input.disable_double_tap = false
     DGESDETECT_DISABLE_DOUBLE_TAP = false
     self.ui:handleEvent(Event:new("SetZoomMode", self.flipping_zoom_mode))
@@ -271,6 +273,7 @@ function ReaderPaging:exitFlippingMode()
     DGESDETECT_DISABLE_DOUBLE_TAP = self.DGESDETECT_DISABLE_DOUBLE_TAP
     Input.disable_double_tap = DGESDETECT_DISABLE_DOUBLE_TAP
     self.flipping_zoom_mode = self.view.zoom_mode
+    self.flipping_scroll_mode = self.view.page_scroll
     DEBUG("restore zoom mode", self.orig_zoom_mode)
     self.ui:handleEvent(Event:new("SetZoomMode", self.orig_zoom_mode))
 end