From 79275d9db409bd2bc6b9985f0ac0a0e1a3ec0d4e Mon Sep 17 00:00:00 2001
From: qwerty287 <80460567+qwerty287@users.noreply.github.com>
Date: Wed, 26 Oct 2022 18:21:08 +0200
Subject: [PATCH] Fix 500 on PR files API (#21602) (#21607)

Fixes an 500 error/panic if using the changed PR files API with pages
that should return empty lists because there are no items anymore.
`start-end` is then < 0 which ends in panic.

Backport https://github.com/go-gitea/gitea/pull/21602

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Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: delvh <dev.lh@web.de>
---
 routers/api/v1/repo/pull.go | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/routers/api/v1/repo/pull.go b/routers/api/v1/repo/pull.go
index f6507dceb..ebb9c0f26 100644
--- a/routers/api/v1/repo/pull.go
+++ b/routers/api/v1/repo/pull.go
@@ -1443,7 +1443,11 @@ func GetPullRequestFiles(ctx *context.APIContext) {
 		end = totalNumberOfFiles
 	}
 
-	apiFiles := make([]*api.ChangedFile, 0, end-start)
+	lenFiles := end - start
+	if lenFiles < 0 {
+		lenFiles = 0
+	}
+	apiFiles := make([]*api.ChangedFile, 0, lenFiles)
 	for i := start; i < end; i++ {
 		apiFiles = append(apiFiles, convert.ToChangedFile(diff.Files[i], pr.HeadRepo, endCommitID))
 	}