Worksheet::toArray exports columns that have formatting but nothing else

[zoltan-vespertool]

Steps to reproduce:

• Create new spreadsheet in Openoffice
• Click on top left button to select the entire sheet
• Enter some data
• Apply some formatting, e.g. bold font or setting column widths
• Save as test.ods
• Open with PhpSpreadsheet
• Export sheet with Worksheet::toArray
• Resulting array has 16384 columns, regardless of what data there is in the cells

Proposed fix is #4642 .