fix list end handling with minimal differences

ffplayout.yml

@@ -4,7 +4,7 @@ general:
         in this case is, to stop ffplayout and start it again. Here we only say when
         it stops, the starting process is in your hand. Best way is a systemd serivce
         on linux. 'stop_threshold' stop ffplayout, if it is async in time above this
-        value.
+        value. A number below 3 can cause unexpected errors.
     stop_threshold: 11
 
 mail:

ffplayout/playlist.py

@@ -334,7 +334,7 @@ class GetSourceFromPlaylist:
             if self.last:
                 seek = self.node['seek'] if self.node['seek'] > 0 else 0
                 delta, _ = get_delta(begin)
-                delta += seek + 1
+                delta += seek + sync_op.threshold
 
             next_start = begin - playlist.start + out + delta
         else: