Also check for GPG_ERR_ASS_CANCELED during an inquire.

Fix pinentry-mode=loopback when cancelling an inquire from scdaemon.
This is similar to commit 4f21f8d but for both protocol command
cancellation and pinentry cancellation.

• agent/call-scd.c (agent_card_pkdecrypt): Check for

GPG_ERR_ASS_CANCELED.
(agent_card_pksign): Ditto.