lib: Fix panic due to closed event subscriptions on shutdown (#8079)

lib/syncthing/auditservice.go

@@ -38,7 +38,11 @@ func (s *auditService) Serve(ctx context.Context) error {
 
 	for {
 		select {
-		case ev := <-sub.C():
+		case ev, ok := <-sub.C():
+			if !ok {
+				<-ctx.Done()
+				return ctx.Err()
+			}
 			enc.Encode(ev)
 		case <-ctx.Done():
 			return ctx.Err()

lib/syncthing/verboseservice.go

@@ -31,7 +31,11 @@ func (s *verboseService) Serve(ctx context.Context) error {
 	defer sub.Unsubscribe()
 	for {
 		select {
-		case ev := <-sub.C():
+		case ev, ok := <-sub.C():
+			if !ok {
+				<-ctx.Done()
+				return ctx.Err()
+			}
 			formatted := s.formatEvent(ev)
 			if formatted != "" {
 				l.Verboseln(formatted)