[pitivi] previewers: Do not forget to call bus.remove_watch

[Thibault Saunier <tsaunier src gnome org>]

commit 0f66cf7b024805f6adcfc4d8a3f41c8997ea30dc
Author: Thibault Saunier <tsaunier gnome org>
Date:   Tue Aug 8 18:56:56 2017 -0400

    previewers: Do not forget to call bus.remove_watch
    
    Otherwise we leak the GstPoll, leading to leaking fds, and exhausting
    avalaible ones.
    
    Fixes T7793

 pitivi/timeline/previewers.py |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/pitivi/timeline/previewers.py b/pitivi/timeline/previewers.py
index 9915f33..7a2e8a9 100644
--- a/pitivi/timeline/previewers.py
+++ b/pitivi/timeline/previewers.py
@@ -705,6 +705,7 @@ class VideoPreviewer(Previewer, Zoomable, Loggable):
             self._thumb_cb_id = None
 
         if self.pipeline:
+            self.pipeline.get_bus().remove_signal_watch()
             self.pipeline.set_state(Gst.State.NULL)
             self.pipeline.get_state(Gst.CLOCK_TIME_NONE)
             self.pipeline = None