[pitivi] utils:pipeline: Fix backtrace

[Thibault Saunier <tsaunier src gnome org>]

commit c34f73983a88e802be28bcbd6623e89667dcb3f4
Author: Thibault Saunier <tsaunier gnome org>
Date:   Mon Jan 19 08:25:28 2015 +0100

    utils:pipeline: Fix backtrace
    
    TypeError: argument of type 'NoneType' is not iterable

 pitivi/utils/pipeline.py |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/pitivi/utils/pipeline.py b/pitivi/utils/pipeline.py
index 3a2c1f7..9602d3b 100644
--- a/pitivi/utils/pipeline.py
+++ b/pitivi/utils/pipeline.py
@@ -606,7 +606,7 @@ class Pipeline(GES.Pipeline, SimplePipeline):
         self._seeker.connect("seek", self._seekCb)
         self._seeker.connect("seek-relative", self._seekRelativeCb)
 
-        if "watchdog" in os.environ.get("PITIVI_UNSTABLE_FEATURES", None):
+        if "watchdog" in os.environ.get("PITIVI_UNSTABLE_FEATURES", ''):
             watchdog = Gst.ElementFactory.make("watchdog", None)
             if watchdog:
                 watchdog.props.timeout = WATCHDOG_TIMEOUT * 1000