PostController: editing a discussion or poll would result in a hidden CategoryID input with an empty value whenever 'Display root categories as headings' was checked. This did not cause issues when editing a regular discussion, which was fortunate, but when editing a poll the form would error out due to a null CategoryID.
Merge branch 'stage' of github.com:vanilla/vanilla into feature/postcontroller-fix
Merge pull request #2000 from vanilla/feature/postcontroller-fix

PostController: editing a discussion or poll would result in a missing CategoryID error
Activity: Add check to target before redirection.
Activity: Refactor IsSafeLink to IsSafeUrl.
Activity: Refactor to IsSafeUrl to not call get twice.
Activity: Improve IsSafeUrl.
Activity: Optimize IsSafeUrl.
Merge branch 'master' into stage
Fix Disqus CSS typo.
Merge pull request #2001 from vanilla/hotfix/burp

Activity: Add check to target before redirection.
Remove the .travis.yml.
Emoji: Fix to use proper path.
Merge branch 'master' of github.com:vanilla/vanilla into stage
Merge branch 'stage' into feature/multisite