Don't assume all comments are created via comment form w/ UI

Here's a small patch that checks whether the notifications_team key is set in the comment array on hook_comment. The problem is that if the comment is posted/created via other means than on the comment form itself, it may not have these values set, and thus notifications_team_update should not get run. For example, if a comment is created with mailhandler/mail2web, notifications_team will wipe out the subscriptions because this array is not set when creating a comment via these modules. This patch just checks whether the array is set, and if it is not, it will not do anything (it won't delete/update the notifications).

Ian