Prevent calendar errors caused by wrong event times

Closes #1301 (closed)

What does this MR do?

Prevents the error that happens during calendar export if the calendar includes an event with an end time that is before the start time. In that case, the end date is set to start date + 1 hour.

Creating events with wrong times is unfortunately still possible. In a future MR the event form needs to be fixed so that these false events can not be created anymore. #1514 (closed) keeps track of that.

How confident are you it won't break things if deployed?

absolutely

How to test

1. Checkout branch locally
2. Login as userbot
3. Create an event in any region or group and set its end time before the start time.
4. Accept the invitation to that event
5. In your profile settings, create a calendar token and try to export the ICS file. It should success without an error.

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• added to the next milestone (see https://gitlab.com/foodsharing-dev/foodsharing/-/milestones, unless it has a "for:Dev" label)
• added an entry to CHANGELOG.md
• added a short text that can be used in the release notes
• Once your MR has been merged, you are responsible to create a testing issue in the Beta Testing forum: https://foodsharing.de/?page=bezirk&bid=734&sub=forum. Please change the MRs label to "state:Beta testing".
  • Consider writing a detailed description in German.
  • Describe in a few sentences, what should be tested from a user perspective.
  • Also mention different settings (e.g. different browsers, roles, ...) how this change can be tested.
  • Be aware, that also non technical people should understand.

Release notes text in German

Closes #1301 (closed)