[QA 4.90.10] "Export to CSV" function doesn't work

Steps to Reproduce:
1: Create a portfolio candidate by clicking "Compute portfolios"
2: Enable the checkbox beside the portfolio and click "Portfolio", "Merge to a single strategy"
3: "PortfolioMerge" is generated in the "Simple strategies" tab.
4: Enable the checkbox beside the "PortfolioMerge" and click "Save", and "Export to CSV".
5: QuantAnalyzer generates only 1KB file that contains one title column and one data column.
That is a bug.


Whereas, If I choose "Save", and "HTML report (.htm)", it generates valid .htm data.
Also, If I choose "Save", and "PDF report (.pdf)", it generates valid .pdf data.