Unset an invalid submitted topic

Authored by SBisson on Tue, Feb 13, 11:48 AM.

Description

Unset an invalid submitted topic

This prevents an array (?topiclist_title[]=foo) from
being treated as a string and added to the DOM and
produce: "PHP Notice: Array to string conversion"

Bug: T186908
Change-Id: I50f3539513b992e11cb78d8e9da60c99c869a7bb