Fix wrong check when create image without data.

The default value of 'locations' is [].So there is a wrong check in
db/sqlalchemy/api.py.
When create an image without data, The function '_image_locations_set'
should not be executed.

Change-Id: Ie4cb29ab0d714d3ce67f717d5eaf641424efa5b7
Closes-bug:#1471080

glance/db/sqlalchemy/api.py

@@ -795,7 +795,7 @@ def _image_update(context, values, image_id, purge_props=False,
         _set_properties_for_image(context, image_ref, properties, purge_props,
                                   session)
 
-        if location_data is not None:
+        if location_data:
             _image_locations_set(context, image_ref.id, location_data,
                                  session=session)
 

glance/tests/functional/db/base.py

@@ -191,6 +191,12 @@ class DriverTests(object):
                   for l in image['locations']]
         self.assertEqual(locations, actual)
 
+    def test_image_create_without_locations(self):
+        locations = []
+        fixture = {'status': 'queued',
+                   'locations': locations}
+        self.db_api.image_create(self.context, fixture)
+
     def test_image_create_with_location_data(self):
         location_data = [{'url': 'a', 'metadata': {'key': 'value'},
                           'status': 'active'},