Fix #1537 and #1702 contact page redirect issues

Redirects to the index page if usergroup limits are about to be
exceeded.
https://github.com/mybb/mybb/issues/1537

And forces the redirects to be displayed.
https://github.com/mybb/mybb/issues/1702
Merge pull request #1703 from Destroy666x/fix1537

Fix #1537 and #1702 contact page redirect issues