Editing a post allows empty message if a file is attached, new posts do not

[martincodeinc]

What steps will reproduce the problem?

Make a new post with no content and a file attached

What is the expected result?

The post is saved

What do you get instead?

The post form says "You need to enter a message"

Additional info

Posting a new message:
The rules in modules/post/models/Post.php is preventing posting an empty message, even when e.g. an image is attached.
You always have to enter one character to get your image posted.
When you look at the validator code in in modules/post/models/forms/PostEditForm.php there seems to be such a mechanism in place to allow empty posts with at least one file attachment when editing an existing message.
Why is this not implemented with new posts?

Editing an existing message:
The rules in modules/post/models/Post.php is overruling the validate function in modules/post/models/forms/PostEditForm.php - and will never touch the validate function.

Q	A
HumHub version	1.15.3
PHP version	8.2
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