bug#43828: invalid date converting from UTC, near DST

[Martin Fido]

I have tzdata version 2020a:

    $ apt-cache policy tzdata
    tzdata:
      Installed: 2020a-0ubuntu0.16.04
      Candidate: 2020a-0ubuntu0.16.04
    ...

    $ zdump -v Australia/Sydney | grep 2020
    Australia/Sydney  Sat Apr  4 15:59:59 2020 UT = Sun Apr  5 02:59:59 2020 
AEDT isdst=1 gmtoff=39600
    Australia/Sydney  Sat Apr  4 16:00:00 2020 UT = Sun Apr  5 02:00:00 2020 
AEST isdst=0 gmtoff=36000
    Australia/Sydney  Sat Oct  3 15:59:59 2020 UT = Sun Oct  4 01:59:59 2020 
AEST isdst=0 gmtoff=36000
    Australia/Sydney  Sat Oct  3 16:00:00 2020 UT = Sun Oct  4 03:00:00 2020 
AEDT isdst=1 gmtoff=39600