[ticket/13117] Correctly define auto increment columns as "NOT NULL" on mysql

Unintended change from 95ab4b3e931521ce3c56068478311f0c04f713cc

PHPBB3-13117
Merge pull request #3003 from nickvergessen/ticket/13117

[ticket/13117] Correctly define auto increment columns as "NOT NULL" on mysql
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/13117] Correctly define auto increment columns as "NOT NULL" on mysql