MAINT: fix DemoController in the image_from_file example (#893)

After the update of traitsui, the ui requires the init() method to return a boolean that indicates whether the initiation has been successful. However, some demos have not been able to adapt to this change such as #889 . This PR aims to fix #889 by adding the boolean return to the demo. closes #889 

Co-authored-by: Chengyu Liu <cyliu@aus552cyliu.local>
Co-authored-by: Corran Webster <cwebster@enthought.com>

chaco/examples/demo/basic/image_from_file.py

@@ -183,6 +183,7 @@ def init(self, info):
         Overridden here to assign the 'view' trait.
         """
         self.view = info.object
+        return True
 
     def save(self, ui_info):
         """