Don't write cols tag when it donesn't exist

src/xlsxworksheet.cpp

@@ -369,6 +369,7 @@ void Worksheet::saveToXmlFile(QIODevice *device)
     //    writer.writeAttribute("x14ac:dyDescent", "0.25");
     writer.writeEndElement();//sheetFormatPr
 
+    if (!m_colsInfo.isEmpty()) {
         writer.writeStartElement("cols");
         foreach (XlsxColumnInfo *col_info, m_colsInfo) {
             writer.writeStartElement("col");
@@ -384,6 +385,7 @@ void Worksheet::saveToXmlFile(QIODevice *device)
             writer.writeEndElement();//col
         }
         writer.writeEndElement();//cols
+    }
 
     writer.writeStartElement("sheetData");
     if (m_dim_rowmax == INT32_MIN) {