End previous live activity when launching a new timer

LeCountdown/Conductor.swift

@@ -137,7 +137,7 @@ class Conductor: ObservableObject {
         DispatchQueue.main.async {
             
             let countdownId = countdown.stringId
-            self._cleanupCurrentTimerIfNecessary(countdownId)
+            self._cleanupPreviousTimerIfNecessary(countdownId)
             
             do {
                 let start = Date()
@@ -171,11 +171,12 @@ class Conductor: ObservableObject {
         }
     }
     
-    fileprivate func _cleanupCurrentTimerIfNecessary(_ timerId: TimerID) {
+    fileprivate func _cleanupPreviousTimerIfNecessary(_ timerId: TimerID) {
         self.removeLiveTimer(id: timerId)
         if let player = self._delayedSoundPlayers[timerId] {
             player.stop() // release resources
         }
+        self._endLiveActivity(timerId: timerId)
     }
     
     func cancelCountdown(id: TimerID) {