[BUG] Hide previous comments doesn't mark all as hidden

[GabeL7r]

When the Terraform plan has multiple comments only the first one gets marked as hidden. I think this is because of the filtering done here: https://github.com/runatlantis/atlantis/pull/994/files#diff-e348084f0b7562996b0bd5d429158e53R177

This should also catch Continued from previous comment.

[lkysow]

Fixed by #1034