[pitivi] project: Fix setting the modification state

[Alexandru Băluț <alexbalut src gnome org>]

commit f1e08f4c90df7a43cc7291384168f1883a7ad85b
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Tue Feb 16 17:34:12 2016 +0100

    project: Fix setting the modification state
    
    When loading a project with missing assets, the app was asking whether
    to save the incomplete loaded project when the user is trying to open
    another.
    
    Differential Revision: https://phabricator.freedesktop.org/D782

 pitivi/project.py |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/pitivi/project.py b/pitivi/project.py
index 4f7f275..661000f 100644
--- a/pitivi/project.py
+++ b/pitivi/project.py
@@ -1401,6 +1401,9 @@ class Project(Loggable, GES.Project):
         return res
 
     def setModificationState(self, state):
+        if not self.loaded:
+            return
+
         self._dirty = state
         if state:
             self.emit('project-changed')