Fix diff view style handling (#36324)

Fix #36323

routers/web/repo/pull.go

@@ -865,7 +865,7 @@ func viewPullFiles(ctx *context.Context, beforeCommitID, afterCommitID string) {
 	ctx.Data["DiffBlobExcerptData"] = &gitdiff.DiffBlobExcerptData{
 		BaseLink:       ctx.Repo.RepoLink + "/blob_excerpt",
 		PullIssueIndex: pull.Index,
-		DiffStyle:      ctx.FormString("style"),
+		DiffStyle:      GetDiffViewStyle(ctx),
 		AfterCommitID:  afterCommitID,
 	}
 	ctx.Data["DiffNotAvailable"] = diffShortStat.NumFiles == 0