scd: Fix PC/SC error handling at apdu_dev_list_start.
* scd/apdu.c (PCSC_E_NO_READERS_AVAILABLE): Add. (pcsc_error_to_sw): Handle PCSC_E_NO_READERS_AVAILABLE. (apdu_dev_list_start): Return error correctly.
- GnuPG-bug-id: T4864
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>