scd: Fix resetting and closing of the reader. (Backported by gniibe)

* scd/command.c (update_card_removed): Do no act on an invalid VRDR.
(do_reset): Ignore apdu_reset error codes for no and inactive card.
Close the reader before setting the slot to -1.
(update_reader_status_file): Notify the application before closing the
reader.

With this change the scd now works as it did in the past. In
particular there is no more endless loop trying to open the reader by
the update_reader_status_file ticker function. That bug basically
blocked all card operations until the scdaemon was killed.