[pitivi/1.0] previewers: Handle empty queue

[Thibault Saunier <tsaunier src gnome org>]

commit 7236ee2573c16930621e81cbfe17dab989fd3cf0
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Mon Jul 9 00:27:59 2018 +0200

    previewers: Handle empty queue

 pitivi/timeline/previewers.py | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
---
diff --git a/pitivi/timeline/previewers.py b/pitivi/timeline/previewers.py
index 9a947b10..b167e033 100644
--- a/pitivi/timeline/previewers.py
+++ b/pitivi/timeline/previewers.py
@@ -558,7 +558,14 @@ class VideoPreviewer(Previewer, Zoomable, Loggable):
         """Creates a missing thumbnail."""
         self._thumb_cb_id = None
 
-        self.position = self.queue.pop(0)
+        try:
+            self.position = self.queue.pop(0)
+        except IndexError:
+            # The queue is empty. Can happen if _update_thumbnails
+            # has been called in the meanwhile.
+            self.stop_generation()
+            return False
+
         self.log("Creating thumb at %s", self.position)
         self.pipeline.seek(1.0,
                            Gst.Format.TIME,