pull requests: wrong line numbers in discussions

[rnwgnr]

Gitea Version

1.16.0+dev-630-g042cac5fe

Git Version

No response

Operating System

No response

How are you running Gitea?

tested on try.gitea.io with a migrated repo

Database

No response

Can you reproduce the bug on the Gitea demo site?

Yes

Log Gist

No response

Description

demo: https://try.gitea.io/murks/Vereinsdokumente/pulls/7

I've created a comment for line 23 in a PR. While everything is fine in the "Files Changed" tab, the text block in the conversation view is off-by-one which brings the comments out of context.

Screenshots

Files Changed tab:

Conversation tab with wrong text section:

[lunny]

So which line is the right one?

[rnwgnr]

Sorry, i've forget to add that information:
The comment has been created for line 23.

If you look at the screen of the Conversation tab you'll notice that the line numbers are adjusted to line 23, but the text is off-by-one. ## §4 Umgang mit der SARS-Cov-2-Pandemie should be line 21 (as shown in the Files Changed tab), but is shown as line 22 in the Conversation view.

[jpraet]

Possibly some corner case in CutDiffAroundLine (https://github.com/go-gitea/gitea/blob/main/modules/git/diff.go#L135)?
I suspect it may have something to do with the \ No newline at end of file.
https://try.gitea.io/murks/Vereinsdokumente/pulls/7.diff

/cc @zeripath