fix calculation of widget height of filechooser

the height of filechooser is provided when creating filechooser
widget since there may be no title as in filemanger which needs
a special title widget to contain filemanger menu.

frontend/ui/downloadmgr.lua

@@ -1,5 +1,6 @@
 local PathChooser = require("ui/widget/pathchooser")
 local UIManager = require("ui/uimanager")
+local Screen = require("device").screen
 local util = require("ffi/util")
 local _ = require("gettext")
 
@@ -20,6 +21,7 @@ function DownloadMgr:chooseDir()
     local download_dir = G_reader_settings:readSetting("download_dir")
     local path_chooser = PathChooser:new{
         title = self.title,
+        height = Screen:getHeight(),
         path = download_dir and (download_dir .. "/..") or lastdir,
         show_hidden = G_reader_settings:readSetting("show_hidden"),
         onConfirm = function(path)

frontend/ui/widget/filechooser.lua

@@ -31,7 +31,6 @@ local FileChooser = Menu:extend{
 
 function FileChooser:init()
     self.width = Screen:getWidth()
-    self.height = Screen:getHeight()
     -- common dir filter
     self.dir_filter = function(dirname)
         for _, pattern in ipairs(self.exclude_dirs) do