libcacard/vcard_emul_nss: don't stop thread when there are no slots
libcacard/vcard_emul_nss: don't stop thread when there are no slots

Signed-off-by: Alon Levy <816c907b754fa7b5d4bb5eb91e0fc01e5510e64d@redhat.com>

SPICE/libcacard,elmarco/libcacard,elmarco/libcacard,SPICE/libcacard