Fix sorting of meetings on dashboard

[bspekker]

Describe the bug
We can observe a case where the ended meetings are not sorted correctly by date.

How to Reproduce
Reproduction so far was not successful. Please contact me or @emanuelschuetze for the specific case.

Expected behavior
Meetings on the dashboard should always be sorted:

1. chronologically by start_date
2. by name (if start_date is the same)