Empty contrib children elements introduced causing load to pmc errors
When editing part and book metadata, select "add editor" / "add author" and don't enter any information, it still creates blank editors / authors that cause load to PMC errors.
See for example chapter ingest failure for cokotestword4:
Chapter : cokotestword4.lanthanum_CO3.1.d69189
ERROR :[2020-12-07 12:10:01]: lanthanum_CO3.xml: STYLE ERROR.
ERROR :[2020-12-07 12:10:01]: surname should not be empty (context: /book-part-wrapper/book-meta/contrib-group/contrib[3]/name/surname )}
INFO :[2020-12-07 12:10:01]: STS ID: 5fce61e92183cf1b2dfab850 TYPE: notice
INFO :[2020-12-07 12:10:01]: lanthanum_CO3-badstyle.XML: <<<= check bad style source here.
INFO :[2020-12-07 12:10:01]: lanthanum_CO3.xml: FAILED [processed in 7.09 sec.]
INFO :[2020-12-07 12:10:01]: STS ID: 5fce61e92183cf1b2dfab851 TYPE: xml_map
INFO :[2020-12-07 12:10:01]: SUMMARY: Number of files successfully processed = 0; with errors = 1; with warnings = 0
INFO :[2020-12-07 12:10:01]: @@SetSessionAttr(nxml)=@@