fix: Save and close taking time when Flex or Icom is not connected

internal/cat/icomserial.go

@@ -444,8 +444,14 @@ func (b *IcomSerial) write(payload ...byte) error {
 
 // recv waits for a frame the reader routed to respCh that satisfies match, or
 // times out. The reader has already discarded echoes and split off scope frames,
-// so recv only ever sees candidate control replies.
+// so recv only ever sees candidate control replies. It also bails out at once if
+// Interrupt() fires (Stop) so an in-flight ReadState — which can be a dozen reads,
+// each up to icomReadTimeout when the rig is slow — doesn't make Stop/Save-&-Close
+// wait several seconds for the poll goroutine to finish.
 func (b *IcomSerial) recv(timeout time.Duration, match func(civ.Decoded) bool) (civ.Decoded, error) {
+	b.dialMu.Lock()
+	cancel := b.dialCancel
+	b.dialMu.Unlock()
 	deadline := time.After(timeout)
 	for {
 		select {
@@ -453,6 +459,8 @@ func (b *IcomSerial) recv(timeout time.Duration, match func(civ.Decoded) bool) (
 			if match(f) {
 				return f, nil
 			}
+		case <-cancel:
+			return civ.Decoded{}, fmt.Errorf("icom: interrupted")
 		case <-deadline:
 			return civ.Decoded{}, fmt.Errorf("icom: timeout waiting for response")
 		}