Fix next video button to support playlist videos

fixes #2523

client/src/app/videos/+video-watch/video-watch.component.ts

@@ -541,7 +541,9 @@ export class VideoWatchComponent implements OnInit, OnDestroy {
   }
 
   private autoplayNext () {
-    if (this.nextVideoUuid) {
+    if (this.playlist) {
+      this.zone.run(() => this.videoWatchPlaylist.navigateToNextPlaylistVideo())
+    } else if (this.nextVideoUuid) {
       this.router.navigate([ '/videos/watch', this.nextVideoUuid ])
     }
   }