[pitivi] clipproperties: Disconnect from the project when it's closed

[Alexandru Băluț <alexbalut src gnome org>]

commit a9058c7498d56829517fd0046cba8c82bd2c7cff
Author: Harish Fulara <harish14143 iiitd ac in>
Date:   Sun Mar 11 21:28:18 2018 +0530

    clipproperties: Disconnect from the project when it's closed
    
    When we open a new project via app menu, the current project gets closed
    but its reference in TransformationProperties class is not set to None.
    
    Closes #2171

 pitivi/clipproperties.py | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/pitivi/clipproperties.py b/pitivi/clipproperties.py
index f18bbbad..3b9b9818 100644
--- a/pitivi/clipproperties.py
+++ b/pitivi/clipproperties.py
@@ -550,6 +550,8 @@ class TransformationProperties(Gtk.Expander, Loggable):
 
         self.app.project_manager.connect_after(
             "new-project-loaded", self._newProjectLoadedCb)
+        self.app.project_manager.connect_after(
+            "project-closed", self.__project_closed_cb)
 
     def _newProjectLoadedCb(self, unused_app, project):
         if self._selection is not None:
@@ -564,6 +566,9 @@ class TransformationProperties(Gtk.Expander, Loggable):
             self._selection.connect('selection-changed', self._selectionChangedCb)
             self._project.pipeline.connect("position", self._position_cb)
 
+    def __project_closed_cb(self, unused_project_manager, unused_project):
+        self._project = None
+
     def _initButtons(self):
         clear_button = self.builder.get_object("clear_button")
         clear_button.connect("clicked", self._defaultValuesCb)