Prevent useless comment fetching for screenshots and file attachments.
Prevent useless comment fetching for screenshots and file attachments.

Screenshots and file attachments without comments weren't having their
_comments variable set, which was causing us to do a fetch later on
for each screenshot and file attachment. We now make sure to always
set _comments in review_detail, preventing these extra, useless fetches.

1tush/reviewboard,beol/reviewboard,brennie/reviewboard,beol/reviewboard,davidt/reviewboard,custode/reviewboard,beol/reviewboard,brennie/reviewboard,davidt/reviewboard,reviewboard/reviewboard,KnowNo/reviewboard,davidt/reviewboard,1tush/reviewboard,sgallagher/reviewboard,bkochendorfer/reviewboard,sgallagher/reviewboard,custode/reviewboard,bkochendorfer/reviewboard,custode/reviewboard,sgallagher/reviewboard,1tush/reviewboard,beol/reviewboard,reviewboard/reviewboard,custode/reviewboard,1tush/reviewboard,brennie/reviewboard,reviewboard/reviewboard,1tush/reviewboard,chipx86/reviewboard,brennie/reviewboard,1tush/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,1tush/reviewboard,KnowNo/reviewboard,KnowNo/reviewboard,davidt/reviewboard,bkochendorfer/reviewboard,KnowNo/reviewboard,bkochendorfer/reviewboard,1tush/reviewboard,1tush/reviewboard,chipx86/reviewboard,chipx86/reviewboard,sgallagher/reviewboard