drawingML: do not write empty schemeClr tags
drawingML: do not write empty schemeClr tags

Change-Id: I8508f00f6af218605d1d43d3efcefbf545387ab8

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core