Fix incorrect rendering csv file when file size is larger than UI.CSV.MaxFileSize (#29653)

Fix #29506

modules/markup/csv/csv.go

@@ -93,9 +93,11 @@ func (Renderer) Render(ctx *markup.RenderContext, input io.Reader, output io.Wri
 		if _, err := tmpBlock.WriteString(html.EscapeString(string(rawBytes))); err != nil {
 			return err
 		}
-		_, err = tmpBlock.WriteString("</pre>")
+		if _, err := tmpBlock.WriteString("</pre>"); err != nil {
 			return err
 		}
+		return tmpBlock.Flush()
+	}
 
 	rd, err := csv.CreateReaderAndDetermineDelimiter(ctx, bytes.NewReader(rawBytes))
 	if err != nil {