Merge pull request 'fix bug #73466' (#249) from fix/bug73466 into hotfix/v8.3.2

Reviewed-on: https://git.onlyoffice.com/ONLYOFFICE/core/pulls/249

Author: ElenaSubbotina

OOXML/XlsxFormat/Worksheets/SheetData.cpp

@@ -2912,6 +2912,8 @@ namespace OOX
                         XLSB::XLWideString str;
                         if(m_oValue.IsInit())
                             str = m_oValue->m_sText;
+                        else
+                            str = L"";
                         *CellRecord << str;
                     }
                     else