Bugfix: File not found errors with f_file_access().

Bugfix: File not found errors with f_file_access().

This is happening because the symbolic link is being followed.
Avoid this behavior by switching to using f_file_access_at().
Set the directory to the current working directory, which happens to be `-100`.

I need to revisit this once I decided on how I am going to handle the CWD of `-100` for the FLL library as a whole.

Ignore file not found errors on access checks.
If the file does not exist, then do not care if the access check for a non-existent file fails.