Detect invalid start and end times
If the user enters an invalid string such as "25:00" into the start time field or the end/due time field, IncidenceDateTime does not detect it, because the QDateTime constructor used by currentStartDateTime() and currentEndDateTime() treats it as "00:00". This patch * detects and reports the error, * uses more specific error messages, * focuses on the erroneous field, and * logs at "debug" level, because the problem isn't very big. CCBUG: 409912