Hide diff stats on empty PRs (#30629)
When a PR is empty, e.g. has neither additions nor deletions, we don't
need to show this:
<img width="125" alt="Screenshot 2024-04-21 at 23 25 38"
src="https://github.com/go-gitea/gitea/assets/115237/0b987eb5-66f5-4b9b-b5aa-7e9e267e9b52">
(cherry picked from commit 0386a42f70d1026c50697b12378f5026a63182b9)
authored by