Multiple non-overlapping Range.merge() calls produce a corrupted XLSX workbook

[VintageHighTech]

Bug description

Description
I'm seeing what appears to be a bug in syncfusion_flutter_xlsio when more than one non-overlapping range is merged.

Expected behaviour
Both merged ranges should be written independently to the workbook.
Merged ranges:

Q61:AD61
R65:W65

Excel should open the workbook without reporting any problems.

Actual behaviour

When two merge() calls are made:
Excel reports that the workbook is corrupted and offers to repair it.
After repair, the two separate merged regions have been combined into a single merged area.
Content from the second merged region is lost.
If either merge() call is removed, the workbook opens correctly.

Environment

• syncfusion_flutter_xlsio: 34.1.32
• Flutter: 3.44.1
• Dart: 3.12.1
• Operating System: Windows 11
• Microsoft Excel: Microsoft 365 Version 2606 (Build 20131.20154)

Steps to reproduce

1. Create a new Workbook.
2. Get the first worksheet.
3. Merge the range Q61:AD61.
4. Merge the non-overlapping range R65:W65.
5. Save the workbook to an .xlsx file.
6. Open the file in Microsoft Excel.

Code sample

Code sample

import 'package:syncfusion_flutter_xlsio/xlsio.dart';

void main() {
  final Workbook workbook = Workbook();
  final Worksheet sheet = workbook.worksheets[0];

  sheet.getRangeByName('Q61:AD61').merge();
  sheet.getRangeByName('R65:W65').merge();

  final List<int> bytes = workbook.saveAsStream();
  workbook.dispose();

  // Save bytes to an .xlsx file.
}

Screenshots or Video

failed_merge.xlsx

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Stack Traces

Stack Traces

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On which target platforms have you observed this bug?

Windows

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