wrong file count in folders

[BrainDamage]

• KOReader version:V2020.01-28-ga2eea88d_2020-02-10
• Device: Kobo Aura H2O2

Issue

File count in folders is inconsistent and/or wrong, there's multiple issues here

Steps to reproduce

first bug:
create an empty directory
enable "show hidden files" in the file manager
the empty directory will show 2 elements, and if new files are dragged in, the offset will be always shifted by 2
I suspect it's counting the '.' current directory and '..' parent path

second issue:
create an empty directory
set "show hidden files" to disabled ( although it's irrelevant since koreader hides .sdr folders regardless )
drag inside a new ebook, never read, never cached
verify item count, it should be 1 if "show hidden files" is disabled, 3 if enabled
open the ebook so it generates a .sdr directory even if it's hidden by the ui
verify item count of the directory, it has been increased by 1
delete the .sdr directory and the count goes back by 1

while it's not technically wrong because the content exists, the count is inconsistent with the displayed elements, making it confusing

[BrainDamage]

second issue still present as of commit de15ab3, but now only when "show hidden files" is disabled

to reproduce:

set "show hidden files" to disabled
create an empty directory
drag inside a new ebook, never read, never cached
verify item count, it should be 1
open the ebook so it generates a .sdr directory even if it's hidden by the ui
verify item count of the directory, it is now 2
delete the .sdr directory and the count goes back to 1