[fix] End of document - go to file browser: swap openFileBrowser() close/open order (#5062)

Fixes #5060.

Cf. 89e002f236/frontend/apps/reader/modules/readermenu.lua (L42-L50) and 89e002f236/frontend/apps/reader/readerui.lua (L711-L718)

frontend/apps/reader/modules/readerstatus.lua

@@ -118,10 +118,10 @@ end
 
 function ReaderStatus:openFileBrowser()
     local FileManager = require("apps/filemanager/filemanager")
+    self.ui:onClose()
     if not FileManager.instance then
         self.ui:showFileManager()
     end
-    self.ui:onClose()
     self.document = nil
 end