fdo#54303: Prevent crash on load.
fdo#54303: Prevent crash on load.

Another simple null pointer check, to save the day.

This unfortunately prevents the properties of the skipped field from
being loaded properly, but it's still better than a immediate crash.

Change-Id: I49398d80eb3bf0834b7e9830ac8be3ac776cb354

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