Don't set audio to ambient while other audioActivity exists

// FREEBIE

SignalMessaging/environment/OWSAudioSession.swift

@@ -40,6 +40,12 @@ public class OWSAudioSession: NSObject {
         
         startAudioActivity(audioActivity)
         
+        guard currentActivities.count == 0 else {
+            // We don't want to clobber the audio capabilities configured by (e.g.) media playback or an in-progress call
+            Logger.info("\(logTag) in \(#function) not touching audio session since another currentActivity exists.")
+            return
+        }
+        
         do {
             try avAudioSession.setCategory(AVAudioSessionCategoryAmbient)
         } catch {