Quietly "saves" invalid event (incidence) start or end times as midnight (particularly affects fr_CA (French Canadian) sub-locale)

After switching from Debian 9 to Kubuntu 19.04 (KOrganizer 5.10.3), I noticed that event edition had broken with regards to times. No matter what start and end times would be entered, saving would store these as midnight. This would also affect existing events; editing these would corrupt times, even if these are left untouched.

After investigation, this turned out to be a complicated issue. Ultimately, this symptom comes from 3 underlying issues. The first element explains why the regression happened at this moment: Qt Core's QLocale changed its short time format for the fr_CA sub-locale from version 29 to 32, from the earlier "23:59" to "23 h 59". This change may be undesirable and while there may be no ticket asking for reversion, I am on it: https://unicode-org.atlassian.net/browse/CLDR-8503

The second element is that the widget used to input start and end times, KTimeComboBox, is very fragile with regards to time formats. It works with the most common, but fails with some which were less tested, like "23 h 59". With such a format, an invalid input mask is generated, and instead of producing a "__ h __" field, the input is initialized to "__ _ __", as reported in KDE ticket #409867: https://bugs.kde.org/show_bug.cgi?id=409867

Due to issue #409867, when the users wants to enter, say, 23:45, incidenceeditor will get back an invalid time string which - if I understand correctly - would be in this example "2345". It is obviously impossible for incidenceeditor to do the right thing, but the third issue is that incidenceeditor does not properly handle this situation. Rather than reporting failure, it quietly "saves" a corrupted time, as reported in KDE ticket #409912: https://bugs.kde.org/show_bug.cgi?id=409912

In the end, none of these issues is in the korganizer package, so this ticket does not request a change to korganizer itself. Its only role is to prevent other users from wasting a huge amount of time debugging. If Launchpad allows assigning a ticket to a certain package while still finding that ticket in lookups for another package, feel free to reassign this to incidenceeditor and mark it as affecting korganizer. Otherwise, this ticket can be closed or its severity decreased once Ubuntu's latest release has one of the causing issues solved.