fdo#63311: Unable to delete text from Shape.
fdo#63311: Unable to delete text from Shape.

This avoids setting null as text to the shape.
[empty_text seems to be the initial value of text for shape
 rather than null - something recent? We also seem to
 export empty <text> entries because of this]

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