Player: Fix playback position of already watched videos (#4731)

Trying to watch an already watched video will make the video start 15 seconds
before the end. This is not very comfortable when listening to music or
watching/listening playlists over and over.

This can be easily tested on any instance with the "Save playback position"
enabled in the Preferences.

Closes issue 3976

assets/js/player.js

@@ -351,7 +351,12 @@ if (video_data.params.save_player_pos) {
     const rememberedTime = get_video_time();
     let lastUpdated = 0;
 
-    if(!hasTimeParam) set_seconds_after_start(rememberedTime);
+    if(!hasTimeParam) {
+      if (rememberedTime >= video_data.length_seconds - 20)
+        set_seconds_after_start(0);
+      else
+        set_seconds_after_start(rememberedTime);
+    }
 
     player.on('timeupdate', function () {
         const raw = player.currentTime();