Fix wrong state of SampleChannelBass by adding userRequestedStop

Before this commit, calling Stop makes playing false, which in turn makes IsAlive false.

Author: hwsmm

osu.Framework/Audio/Sample/SampleChannelBass.cs

@@ -40,6 +40,12 @@ public override bool Playing
         /// </summary>
         private volatile bool userRequestedPlay;
 
+        /// <summary>
+        /// <c>true</c> if the user last called <see cref="Stop"/>.
+        /// <c>false</c> if the user last called <see cref="Play"/> or this channel finished playback.
+        /// </summary>
+        private volatile bool userRequestedStop;
+
         /// <summary>
         /// Whether the playback start has been enqueued.
         /// </summary>
@@ -55,6 +61,8 @@ public override bool Looping
             }
         }
 
+        public override bool IsAlive => base.IsAlive && (Playing || userRequestedStop);
+
         private bool hasChannel => channel != 0;
 
         public override ChannelAmplitudes CurrentAmplitudes => (bassAmplitudeProcessor ??= new BassAmplitudeProcessor(this)).CurrentAmplitudes;
@@ -99,8 +107,13 @@ protected override void UpdateState()
                         playing = true;
                         break;
 
+                    case PlaybackState.Paused when userRequestedStop:
+                        playing = false;
+                        break;
+
                     default:
                         playing = false;
+                        userRequestedStop = false;
                         break;
                 }
             }
@@ -119,6 +132,8 @@ public override void Play()
         {
             userRequestedPlay = true;
 
+            userRequestedStop = false;
+
             // Pin Playing and IsAlive to true so that the channel isn't killed by the next update. This is only reset after playback is started.
             enqueuedPlaybackStart = true;
 
@@ -138,6 +153,8 @@ public override void Stop()
         {
             userRequestedPlay = false;
 
+            userRequestedStop = true;
+
             base.Stop();
 
             EnqueueAction(() =>