Startup: Unbreak last_file when the file is missing

Fix #9887, likely a regression since #9669

frontend/ui/uimanager.lua

@@ -825,6 +825,23 @@ function UIManager:unsetRunForeverMode()
     self._gated_quit = self.quit
 end
 
+-- Ignore an empty window stack *once*; for startup w/ a missing last_file shenanigans...
+function UIManager:runOnce()
+    -- We don't actually want to call self.quit, and we need to deal with a bit of trickery in there anyway...
+    self._gated_quit = function()
+        -- We need this set to break the loop in UIManager:run()
+        self._exit_code = 0
+        -- And this is to break the loop in UIManager:handleInput()
+        return true
+    end
+    -- The idea being that we want to *return* from this run call, but *without* quitting.
+    -- NOTE: This implies that calling run multiple times across a single session *needs* to be safe.
+    self:run()
+    -- Restore standard behavior
+    self:unsetRunForeverMode()
+    self._exit_code = nil
+end
+
 --[[--
 Transmits an @{ui.event.Event|Event} to active widgets, top to bottom.
 Stops at the first handler that returns `true`.

reader.lua

@@ -271,15 +271,11 @@ end
 local exit_code
 if file then
     local ReaderUI = require("apps/reader/readerui")
-    UIManager:nextTick(function()
-        ReaderUI:showReader(file)
-    end)
+    ReaderUI:showReader(file)
     exit_code = UIManager:run()
 elseif directory then
     local FileManager = require("apps/filemanager/filemanager")
-    UIManager:nextTick(function()
-        FileManager:showFiles(directory)
-    end)
+    FileManager:showFiles(directory)
     exit_code = UIManager:run()
 else
     local QuickStart = require("ui/quickstart")
@@ -290,47 +286,38 @@ else
 
     if start_with == "last" and last_file and lfs.attributes(last_file, "mode") ~= "file" then
         UIManager:show(retryLastFile())
-        -- no exit code as something else will be run after this.
-        UIManager:run()
+        -- We'll want to return from this without actually quitting,
+        -- so this is a slightly mangled UIManager:run() call to coerce the main loop into submission...
+        -- We'll call :run properly in either of the following branches once returning.
+        UIManager:runOnce()
     end
     if start_with == "last" and last_file then
         local ReaderUI = require("apps/reader/readerui")
-        UIManager:nextTick(function()
-            -- Instantiate RD
-            ReaderUI:showReader(last_file)
-        end)
+        -- Instantiate RD
+        ReaderUI:showReader(last_file)
         exit_code = UIManager:run()
     else
         local FileManager = require("apps/filemanager/filemanager")
-        local home_dir =
-            G_reader_settings:readSetting("home_dir") or Device.home_dir or lfs.currentdir()
-        UIManager:nextTick(function()
-            -- Instantiate FM
-            FileManager:showFiles(home_dir)
-        end)
+        local home_dir = G_reader_settings:readSetting("home_dir") or Device.home_dir or lfs.currentdir()
+        -- Instantiate FM
+        FileManager:showFiles(home_dir)
         -- Always open FM modules on top of filemanager, so closing 'em doesn't result in an exit
         -- because of an empty widget stack, and so they can interact with the FM instance as expected.
         if start_with == "history" then
             local FileManagerHistory = require("apps/filemanager/filemanagerhistory")
-            UIManager:nextTick(function()
-                FileManagerHistory:new{
-                    ui = FileManager.instance,
-                }:onShowHist()
-            end)
+            FileManagerHistory:new{
+                ui = FileManager.instance,
+            }:onShowHist()
         elseif start_with == "favorites" then
             local FileManagerCollection = require("apps/filemanager/filemanagercollection")
-            UIManager:nextTick(function()
-                FileManagerCollection:new{
-                    ui = FileManager.instance,
-                }:onShowColl("favorites")
-            end)
+            FileManagerCollection:new{
+                ui = FileManager.instance,
+            }:onShowColl("favorites")
         elseif start_with == "folder_shortcuts" then
             local FileManagerShortcuts = require("apps/filemanager/filemanagershortcuts")
-            UIManager:nextTick(function()
-                FileManagerShortcuts:new{
-                    ui = FileManager.instance,
-                }:onShowFolderShortcutsDialog()
-            end)
+            FileManagerShortcuts:new{
+                ui = FileManager.instance,
+            }:onShowFolderShortcutsDialog()
         end
         exit_code = UIManager:run()
     end
@@ -342,8 +329,10 @@ local function exitReader()
     local ko_exit = os.getenv("KO_EXIT_CODE")
     if ko_exit then
         local fo = io.open(ko_exit, "w+")
-        fo:write(tostring(exit_code))
-        fo:close()
+        if fo then
+            fo:write(tostring(exit_code))
+            fo:close()
+        end
     end
 
     local ReaderActivityIndicator =