Uploader Gallery tab is empty if draft post has not been saved

[tellyworth]

1. New Post
2. Without entering a post title or text or anything else, click the Add An Image button
3. Upload some images, but don't click Save or Insert
4. Click the Gallery tab

Expected: the gallery tab should list the images you just uploaded.

Actual: the gallery tab is empty except for a Save All Changes button.

[tellyworth]

The bug is in the code at the top of get_media_items(). The code that fetches images there is conditional on get_post($post_id) - since the draft post has not yet been created, the conditional fails.

The patch fixes it. It appears not to break anything else but could use more regression testing.

[ryan]

(In [7650]) Fix image fetching in get_media_items(). Props tellyworth. fixes #6657 for 2.5

[ryan]

(In [7651]) Fix image fetching in get_media_items(). Props tellyworth. fixes #6657 for trunk