- If you attempted to get a branch feed on a empty repository, it would
result in a panic as the code expects that the branch exists.
- `context.RepoRefByType` would normally already 404 if the branch
doesn't exist, however if a repository is empty, it would not do this
check.
- Fix bug where `/atom/branch/*` would return a RSS feed.
(cherry picked from commit d27bcd98a4)
(cherry picked from commit c58566403d)
(cherry picked from commit b8b3f6ab8b)
(cherry picked from commit 195520100b)
(cherry picked from commit 6e417087dd)
(cherry picked from commit ff91e5957a)
(cherry picked from commit 6626d5cc75)
(cherry picked from commit 62f8ab793b)
(cherry picked from commit e5bbf1a2d0)
(cherry picked from commit f5b8c8edea)
(cherry picked from commit 50948fa11b)
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