Backport. See #20910: NOT NULL column reported as NULL in SHOW FIELDS or INFORMATION_SCHEMA


mysql-test/r/type_ranges.result:
  Fix for bug #22377: iNCONSISTENCY WITH null
    - results adjusted.
mysql-test/r/type_timestamp.result:
  Fix for bug #22377: iNCONSISTENCY WITH null
    - results adjusted.
sql/sql_show.cc:
  Fix for bug #22377: iNCONSISTENCY WITH null
    - as NULL values cannot be stored in 'timestamp not null' fields,
      don't make an exception for them.