Reject '0000-00-00 01:01:01' dates.


mysql-test/r/date_formats.result:
  Fix for bug #21789: DATETIME with 0000-00-00 11:22:33 should be invalid, but is accepted 
    - test results adjusted.
sql-common/my_time.c:
  Fix for bug #21789: DATETIME with 0000-00-00 11:22:33 should be invalid, but is accepted 
    - don't allow dates with NULL date part and not NULL time part.