player/Thread: pause all outputs in single mode

This mostly affects the Pulse output plugin which needs to "cork" the
stream (closes #278).

NEWS

@@ -1,6 +1,8 @@
 ver 0.20.20 (not yet released)
 * protocol
   - fix "modified-since" filter regression
+* output
+  - pulse: cork stream when paused due to "single" mode
 * decoder
   - dsdiff, dsf: support more MIME types
   - dsdiff, dsf: allow 4 MB ID3 tags

src/player/Thread.cxx

@@ -950,6 +950,7 @@ Player::SongBorder()
 	const bool border_pause = pc.LockApplyBorderPause();
 	if (border_pause) {
 		paused = true;
+		pc.outputs.Pause();
 		idle_add(IDLE_PLAYER);
 	}
 }