Recurring occurrences not displayed correctly in week view

While testing changes in pull request 88 (https://github.com/llazzaro/django-scheduler/pull/86), I noticed some cases where occurrences of recurring events were still not displayed correctly in week view. An occurrence split over two days was only shown on one of those days.
The problem was that o_starts was being overwritten when multiple rule matches were found. Turning o_starts into a list allows it hold these multiple rule matches.