Let the readerstatus thread wait on gpg-agent

When Kleopatra is started the readerstatus thread may check
for smartcards before the gpg-agent and scdaemon are started
which can take a while, especially on Windows. So we now
handle the GPG_ERR_ASS_CONNECT_FAILED and wait for it to
come up. GnuPG itself does something similar.
2 jobs for master in 16 minutes and 2 seconds (queued for 32 minutes and 37 seconds)