Partly revert "shl: handle pathconf() errors"

This partly reverts commit 41e76d11dff6dd9bc08bf829751f9634f32cdd38. I
removed the "superfluous" errno-handling, which in fact is needed. Turns
out pathconf() might leave errno unchanged.

Reported-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>