Check for existence of property before retrieving its value
Check for existence of property before retrieving its value

Is[Empty]PresentationObject prop seems not to be set in Calc/Writer
shape objects and retrieving its value throws an exception.
This fixes export of xlsx docs with embedded pics/charts.

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