Actually play the default notification sound.

Fixes #3912
// FREEBIE

src/org/thoughtcrime/securesms/notifications/AbstractNotificationBuilder.java

@@ -45,8 +45,8 @@ public abstract class AbstractNotificationBuilder extends NotificationCompat.Bui
     String ledBlinkPatternCustom = TextSecurePreferences.getNotificationLedPatternCustom(context);
     String[] blinkPatternArray   = parseBlinkPattern(ledBlinkPattern, ledBlinkPatternCustom);
 
-    if      (ringtone != null)                       setSound(ringtone);
-    else if (TextUtils.isEmpty(defaultRingtoneName)) setSound(Uri.parse(defaultRingtoneName));
+    if      (ringtone != null)                        setSound(ringtone);
+    else if (!TextUtils.isEmpty(defaultRingtoneName)) setSound(Uri.parse(defaultRingtoneName));
 
     if (vibrate == RecipientPreferenceDatabase.VibrateState.ENABLED ||
         (vibrate == RecipientPreferenceDatabase.VibrateState.DEFAULT && defaultVibrate))