Use correct aspect-ratio for shot thumbnails.

attract/shots/routes.py

@@ -45,6 +45,11 @@ def for_project(project, attract_props, task_id=None, shot_id=None):
         else:
             shot._thumbnail = thumb_placeholder
 
+        # The placeholder can be shown quite small, but otherwise the aspect ratio of
+        # the actual thumbnail should be taken into account. Since it's different for
+        # each project, we can't hard-code a proper height.
+        shot._thumbnail_height = '30px' if shot._thumbnail is thumb_placeholder else 'auto'
+
     tasks_for_shots = current_attract.shot_manager.tasks_for_shots(
         shots,
         attract_props.task_types.attract_shot,