scd: Fix use case of PC/SC.
* scd/apdu.c (apdu_open_reader): Add an argument APP_EMPTY. When CCID driver fails to open, try PC/SC if APP is nothing. * scd/app.c (select_application): Supply arg if APP is nothing.
After scanning available card readers by CCID driver, scdaemon should
try PC/SC service if no APP is registered yet. Also, when the slot
is allocated for PC/SC (ccid.handle==NULL), it should not call
ccid_compare_BAI, otherwise scdaemon crashes.