[gnome-music/wip/mschraal/player-factor-out-gstreamer] player: Fix None duration

[Marinus Schraal <mschraal src gnome org>]

commit 57fa7a298d1c864fc3c56c52d0f621d599182487
Author: Marinus Schraal <mschraal gnome org>
Date:   Sun Feb 18 09:19:15 2018 +0100

    player: Fix None duration

 gnomemusic/player.py | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/gnomemusic/player.py b/gnomemusic/player.py
index 8e67ef7..5bedabe 100644
--- a/gnomemusic/player.py
+++ b/gnomemusic/player.py
@@ -642,6 +642,9 @@ class Player(GObject.GObject):
             utils.seconds_to_string(seconds))
 
         duration = self._player.duration
+        if duration is None:
+            return
+
         position = self._player.position
         if position > 0:
             self.played_seconds += self._seconds_period / 1000