Increase assert coverage of OUStringBuffer arguments
Increase assert coverage of OUStringBuffer arguments

Only covers arguments that can be validated with a simple
comparison, and does not attempt validation of arguments which
would require calculation of the length of a string inline

Change-Id: I8a29c8743b47efe3dd45897a1f1371191a5ddb62
Signed-off-by: Stephan Bergmann <05c31e1673f7a15a4f0f5429fb1e32d6e84bebe3@redhat.com>

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