Added streamlock to disable refreshNextTimer() while streaming. Fixed bug in HLS Livestream Media Handler.

www/js/channel/mediaHandler.js

@@ -605,10 +605,15 @@ class hlsLiveStreamHandler extends hlsBase{
         //Call derived method
         super.onSeek(event);
 
+        //If we stopped playing the video
+        if(this.video == null){
+            //Don't worry about it
+            return;
+        }
+
         //Calculate distance to end of stream
         const difference = this.video.duration - this.video.currentTime;
 
-
         //If we where buffering under sync lock
         if(this.reSync){
             //Set reSync to false