error when no slots defined

[Michael Hall]

Traceback (most recent call last):
  File "/srv/summit.ubuntu.com/summit/schedule/render.py", line 304, in debug
    return self.as_html()
  File "/srv/summit.ubuntu.com/summit/schedule/render.py", line 381, in as_html
    for date in self.dates).seconds / 30
ValueError: max() arg is an empty sequence

[Chris Johnston (cjohnston)]

Marking low as this only matters until the slots are created.

[Chris Johnston (cjohnston)]

This should just need to check to see if slots are defined, if slots aren't defined, return a message saying as such.

[José Antonio Rey (jose)]

Needs to be re-confirmed, as the file has changed lately.