Family timeline error when dates are not Gregorian

[SNoiraud]

Fixes #12525

[Nick-Hall]

Both arguments of a Span are already converted to the Gregorian calendar. See line 80 in the date code. I'm not sure why this fix necessary.

[SNoiraud]

Both arguments of a Span are already converted to the Gregorian calendar. See line 80 in the date code. I'm not sure why this fix necessary.

Yes, I saw that but when we have a french republican date in one event, this is not done. I think we have the same problem when we have different calendars in the event list.

[Nick-Hall]

@SNoiraud The actual bug was with the way the dates were being swapped for negative spans. The swapped dates were taken from the unconverted parameters. I have created PR #1332 with an alternative fix. Please test if you have time, but it works for me.