Make sure a commenter doesn't receive a blank screen when comment is rejected

[solarissmoke]

In the last few changes to wp-comments-post the following action hooks have been added ahead of the pre_comment_on_post action hook:

• comment_on_trash

• comment_on_draft

• comment_on_password_protected

However, none of these hooks have default actions associated with them, which means that on a default install, if someone manages to post a comment on a trashed/draft/protected post, they get a blank screen without any explanation of what went wrong.

I think there should be some default actions here, or some default behaviour in between the action hook and the exit statements.

Proposed patch to follow.

[solarissmoke]

xref ​#11286 for the 403 status header issue. There is no reason WP should return a 500 status error in these cases.

[solarissmoke]

Whoops, it looks like proposed patch for #11286 addresses these issues, so I'll just pursue this there.