code:clash/0: match correct return value from erl_prim_loader:list_dir/1

[Tuncer Ayaz]

Fix the error introduced in 49da83 while correcting another
code:clash/0 issue.

Also update and extend the tests in kernel/code_SUITE:clash/1.

git fetch git://github.com/tuncer/otp.git code_clash_filter_error