Apply image_downsize filter before wp_attachment_is_image check in image_downsize function

[jbrinley]

The function image_downsize in wp-include/media.php calls wp_attachment_is_image, which must return true before applying the image_downsize filter. By moving the call to the image_downsize filter to the beginning of the function, plugins (let's say, for example, the  Custom Thumbnails plugin) can return representations of non-image media.

The only possible negative consequence that I can see: plugin writers can't assume that the image_downsize filter will only be called for images (but I don't know that they should assume that, anyway).

Patch for image_downsize in wp-includes/media.php

+1

Punting due to time constraints. Media changes planned for 2.9/3.0.

a very similar ticket that got closed a week ago or so: #9672

Closing due to lack of traction. Can be reopened if anyone wants to passionately advocate for it.