Sanitize negative status count on APContact

Sanitize negative status count on APContact

Similar to PR #10499, Mastodon apparently has some counting flaws and
can present a negative status count for a user, causing Friendica to
fail (at least under PHP 8) with:

[20-Jul-2021 16:35:18 UTC] PHP Fatal error:  Uncaught PDOException: SQLSTATE[22003]: Numeric value out of range: 1264 Out of range value for column 'statuses_count' at row 1 in /home/friendicadev/friendica/src/Database/Database.php:560
Stack trace:
  thrown in /home/friendicadev/friendica/src/Database/Database.php on line 560

This change prevents values lower than 0 from being assigned to
statuses_count.