[#3820] Fix problem with non unicode strings in feed creation

390dae8 tried to fix this problem, but it
only fixed it in some cases. In some of the cases, the `escape` function
would return a `str` instead of a `unicode` which wouldn't be converted
correctly, before calling the _write method on the `XMLGenerator`.

akvo/rsr/feeds.py

@@ -45,7 +45,7 @@ def escape(data, entities={}):
     bit = data[start:]
     bit = __escape(bit, entities)
     bits.extend(bit)
-    data = ''.join(bits)
+    data = u''.join(bits)
     return data
 
 

akvo/rsr/tests/test_feeds.py

@@ -17,6 +17,8 @@ def test_updates_feed(self):
         title = u'Update de développement'
         text = 'What an amazing update!'
         self.create_project_update(project, user, title, text)
+        empty_title = ''
+        self.create_project_update(project, user, empty_title, text)
 
         response = self.c.get('/rss/updates/{}'.format(project.pk), follow=True)