chore: more luacheck fixes

.luacheckrc

@@ -85,6 +85,7 @@ read_globals = {
     "KOBO_SCREEN_SAVER",
     "KOBO_SCREEN_SAVER_LAST_BOOK",
     "NETWORK_PROXY",
+    "DUSE_TURBO_LIB",
     "cre",
     "lfs",
     "lipc",

frontend/apps/filemanager/filemanager.lua

@@ -66,7 +66,7 @@ function FileManager:init()
     }
     self.file_chooser = file_chooser
 
-    function file_chooser:onFileSelect(file)
+    function file_chooser:onFileSelect(file)  -- luacheck: ignore
         local ReaderUI = require("apps/reader/readerui")
         ReaderUI:showReader(file)
         return true
@@ -78,8 +78,7 @@ function FileManager:init()
     local deleteFile = function(file) self:deleteFile(file) end
     local fileManager = self
 
-    function file_chooser:onFileHold(file)
+    function file_chooser:onFileHold(file)  -- luacheck: ignore
-        --DEBUG("hold file", file)
         local buttons = {
             {
                 {

frontend/ui/uimanager.lua

@@ -6,7 +6,6 @@ local Geom = require("ui/geometry")
 local util = require("ffi/util")
 local DEBUG = require("dbg")
 local _ = require("gettext")
-local ffi = require("ffi")
 
 local MILLION = 1000000
 
@@ -323,8 +322,8 @@ function UIManager:_checkTasks()
     local wait_until = nil
 
     while true do
-        st_size = #self._task_queue
+        local nu_task = #self._task_queue
-        if st_size == 0 then
+        if nu_task == 0 then
             -- all tasks checked
             break
         end

frontend/ui/widget/filechooser.lua

@@ -4,7 +4,6 @@ local Menu = require("ui/widget/menu")
 local Screen = require("device").screen
 local Device = require("device")
 local util = require("ffi/util")
-local DEBUG = require("dbg")
 local _ = require("gettext")
 local ffi = require("ffi")
 ffi.cdef[[

frontend/ui/widget/imagewidget.lua

@@ -58,7 +58,7 @@ function ImageWidget:_loadfile()
         else
             -- cache this image
             DEBUG("cache", hash)
-            local cache = ImageCacheItem:new{
+            cache = ImageCacheItem:new{
                 bb = Mupdf.renderImageFile(self.file, self.width, self.height),
             }
             cache.size = cache.bb.pitch * cache.bb.h * cache.bb:getBpp() / 8