Fix incorrect viewed files counter if file has changed (#36009)

File changes since last review didn't decrease the viewed files counter

---
<img width="440" height="178" alt="image"
src="https://github.com/user-attachments/assets/da34fcf4-452f-4f71-8da2-97edbfc31fdd"
/>

Also reported here ->
https://github.com/go-gitea/gitea/issues/35803#issuecomment-3567850285

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Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

routers/web/repo/pull_review.go

@@ -331,7 +331,7 @@ func UpdateViewedFiles(ctx *context.Context) {
 		updatedFiles[file] = state
 	}
 
-	if err := pull_model.UpdateReviewState(ctx, ctx.Doer.ID, pull.ID, data.HeadCommitSHA, updatedFiles); err != nil {
+	if _, err := pull_model.UpdateReviewState(ctx, ctx.Doer.ID, pull.ID, data.HeadCommitSHA, updatedFiles); err != nil {
 		ctx.ServerError("UpdateReview", err)
 	}
 }