Fix some trivial problems (go-gitea#34237)

1. Using existing "content" variable in `swift.go`
2. Do not report 500 server error in `GetPullDiffStats` middleware,
otherwise a PR missing ref won't be able to view.
3. Fix the abused "label button" when listing commits, there was too
much padding space, see the screenshot below.

(cherry picked from commit ba0deab)

Author: wxiaoguang

routers/api/packages/swift/swift.go

@@ -304,7 +304,7 @@ func formFileOptionalReadCloser(ctx *context.Context, formKey string) (io.ReadCl
 	if content == "" {
 		return nil, nil
 	}
-	return io.NopCloser(strings.NewReader(ctx.Req.FormValue(formKey))), nil
+	return io.NopCloser(strings.NewReader(content)), nil
 }
 
 // UploadPackageFile refers to https://github.com/swiftlang/swift-package-manager/blob/main/Documentation/PackageRegistry/Registry.md#endpoint-6

routers/web/repo/pull.go

@@ -401,22 +401,23 @@ func setMergeTarget(ctx *context.Context, pull *issues_model.PullRequest) {
 
 // GetPullDiffStats get Pull Requests diff stats
 func GetPullDiffStats(ctx *context.Context) {
+	// FIXME: this getPullInfo seems to be a duplicate call with other route handlers
 	issue, ok := getPullInfo(ctx)
 	if !ok {
 		return
 	}
 	pull := issue.PullRequest
 
 	mergeBaseCommitID := GetMergedBaseCommitID(ctx, issue)
-
 	if mergeBaseCommitID == "" {
 		ctx.NotFound("PullFiles", nil)
 		return
 	}
 
+	// do not report 500 server error to end users if error occurs, otherwise a PR missing ref won't be able to view.
 	headCommitID, err := ctx.Repo.GitRepo.GetRefCommitID(pull.GetGitRefName())
 	if err != nil {
-		ctx.ServerError("GetRefCommitID", err)
+		log.Error("Failed to GetRefCommitID: %v, repo: %v", err, ctx.Repo.Repository.FullName())
 		return
 	}