When fetching a list resource, the serialize_object_list was calling

serialize_object for each item in the list but passing the request as

a positional argument instead of a keyword argument. This works fine for

just about everything, but the current implementation of Review Board's

MarkdownFieldsMixin attempts to pull the request out of a kwargs dict,

and so it was failing to find it, resulting in a serialized payload that

did not include any of the requested text types.
The result of this was that the review dialog was not able to access the

raw (or even rendered) text for comments, and so clicking edit on a

comment would open up a blank editor. This bug seems likely to have been

exposed when we changed the inline editors in the review dialog to

use the new (non-jquery-ui) implementation for inline editors, which

also streamlined the way we fetch the comment data.
Ideally we should fix up every version of serialize_object to enforce

that the request parameter is a kwarg, but that's a much larger change

across multiple codebases, so I wanted to fix the bug in isolation

first.

Opened the review dialog with an existing review and was able to edit

comments properly.