[ticket/13048] Only update session_page if request is not ajax

PHPBB3-13048
Merge pull request #2930 from Senky/ticket/13048

[ticket/13048] AJAX requests are being stored to session_page

* Senky/ticket/13048:
  [ticket/13048] Only update session_page if request is not ajax
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/13048] Only update session_page if request is not ajax