project: Emit "rendering-settings-changed" when the pixel aspect ratio changes

Otherwise aspect ratio changes would not always get applied.

Fixes bug #721973

pitivi/project.py

@@ -708,7 +708,8 @@ class Project(Loggable, GES.Project):
 
     @videopar.setter
     def videopar(self, value):
-        self.set_video_restriction_value("pixel-aspect-ratio", value)
+        if self.set_video_restriction_value("pixel-aspect-ratio", value):
+            self._emitChange("rendering-settings-changed", "pixel-aspect-ratio", value)
 
     @property
     def aspect_ratio(self):