Treat pcsc::Error::NoSmartcard as a "YubiKey disconnected" error

Some SmartCard readers report this error when no SmartCard is inserted,
so we need to check for it when filtering for connected YubiKeys (along
with `pcsc::Error::RemovedCard` which some _other_ SmartCard readers
report instead).

Closes str4d/age-plugin-yubikey#81.

src/key.rs

@@ -41,7 +41,7 @@ pub(crate) fn is_connected(reader: Reader) -> bool {
 pub(crate) fn filter_connected(reader: &Reader) -> bool {
     match reader.open() {
         Err(yubikey::Error::PcscError {
-            inner: Some(pcsc::Error::RemovedCard),
+            inner: Some(pcsc::Error::NoSmartcard | pcsc::Error::RemovedCard),
         }) => {
             warn!(
                 "{}",