message: Monitoring: Silence details page: Display `-` when no Firing Alerts
  When the silence did not match any alerts, the Firing Alerts field was
  blank. It should display `-` instead.
diff: @@ -253,6 +253,10 @@ const SeverityBadge: React.FC<{ severity: string }> = ({ severity }) =>
  );
  const SeverityCounts: React.FC<{ alerts: Alert[] }> = ({ alerts }) => {
  + if (_.isEmpty(alerts)) {
  + return <>-</>;
  + }
  +
  const counts = _.countBy(alerts, (a) => {
  const { severity } = a.labels;
  return severity === AlertSeverity.Critical || severity === AlertSeverity.Warning
  @@ -418,7 +422,7 @@ const SilenceTableRow: RowFunction<Silence> = ({ index, key, obj, style }) => {
  </div>
  </TableData>
  <TableData className={tableSilenceClasses[1]}>
  - {_.isEmpty(firingAlerts) ? '-' : <SeverityCounts alerts={firingAlerts} />}
  + <SeverityCounts alerts={firingAlerts} />
  </TableData>
  <TableData className={classNames(tableSilenceClasses[2], 'co-break-word')}>
  <SilenceState silence={obj} />
  