Reader: add open next file in folder to Dispatcher (#9916)

Closes https://www.mobileread.com/forums/showthread.php?t=350683.

frontend/apps/reader/modules/readerstatus.lua

@@ -91,7 +91,7 @@ function ReaderStatus:onEndOfBook()
                     text = _("Open next file"),
                     enabled = collate,
                     callback = function()
-                        self:openNextFile(self.document.file)
+                        self:onOpenNextDocumentInFolder()
                         UIManager:close(choose_action)
                     end,
                 },
@@ -141,7 +141,7 @@ function ReaderStatus:onEndOfBook()
             UIManager:close(info)
             -- Delay until the next tick, as this will destroy the Document instance, but we may not be the final Event caught by said Document...
             UIManager:nextTick(function()
-                self:openNextFile(self.document.file)
+                self:onOpenNextDocumentInFolder()
             end)
         else
             UIManager:show(InfoMessage:new{
@@ -183,12 +183,12 @@ function ReaderStatus:openFileBrowser()
     end
 end
 
-function ReaderStatus:openNextFile(next_file)
+function ReaderStatus:onOpenNextDocumentInFolder()
     local FileManager = require("apps/filemanager/filemanager")
     if not FileManager.instance then
         self.ui:showFileManager()
     end
-    next_file = FileManager.instance.file_chooser:getNextFile(next_file)
+    local next_file = FileManager.instance.file_chooser:getNextFile(self.document.file)
     FileManager.instance:onClose()
     if next_file then
         self.ui:switchDocument(next_file)

frontend/dispatcher.lua

@@ -109,6 +109,7 @@ local settingsList = {
     folder_shortcuts = {category="none", event="ShowFolderShortcutsDialog", title=_("Folder shortcuts"), filemanager=true, separator=true},
 
     -- reader settings
+    open_next_document_in_folder = {category="none", event="OpenNextDocumentInFolder", title=_("Open next document in folder"), reader=true, separator=true},
     toggle_status_bar = {category="none", event="TapFooter", title=_("Toggle status bar"), reader=true, separator=true},
     prev_chapter = {category="none", event="GotoPrevChapter", title=_("Previous chapter"), reader=true},
     next_chapter = {category="none", event="GotoNextChapter", title=_("Next chapter"), reader=true},
@@ -282,6 +283,8 @@ local dispatcher_menu_order = {
     "folder_shortcuts",
 
     -- reader
+    "open_next_document_in_folder",
+
     "show_config_menu",
     "toggle_status_bar",