columnDimension: autoSize for default not working properly if first row has merged cells

Hi,

i have a problem with {columnDimension: {default: {autoSize: true}}} of a xlssheet if the first xlsrow has only merged xlscells. The determination of the columsn doesn't work properly, because only the merged cell is recognized. I think it would be better, if in this case more then the first row is used to set the columnDimension  for the defined/existing columns.
