Fix incorrectly calculating the number of issue counts.

The query for calculating the number of issues led to duplicate results,
which could cause the returned issue count to be abnormally high.

This only happened when reviewing more than one type of thing. For
example, a diff and a file attachment, instead of just a diff or just a
file attachment.

The reason is that the query would return one result for each comment,
but that result would contain issue counts for each type of comment. So,
if commenting on 2 diffs and 1 file attachment, there may be a result
for diff comment 1, and diff comment 2, but both may include the issue
status for file attachment comment 1 as well.

What we needed to do was filter out comment entries we've already seen.
To do this, we request the comment IDs along with the issue statuses.
During processing of issue statuses, we check and see if the comment ID
for the status is one we've already seen. If so, we'll skip that issue
status.