Code changes and unit test to check no empty font name is exported

Problem Description:
In fontTable.xml, empty font name gets exported.
So while exporting check no empty font name is exported.

Conflicts:
	sw/qa/extras/ooxmlexport/ooxmlexport.cxx
Reviewed on:
	https://gerrit.libreoffice.org/6319

Change-Id: Icaa58d23b7754925291867b4c9557c8232f77d69