Rogue placeholder attribute resulting in bizzare triples

[alliyya]

See comment on GitLab ticket: https://gitlab.com/calincs/conversion/metadata-conversion/-/issues/50#note_937029225

A malformed URI is resulting in numerous properties incorrectly being assigned to it. http://cwrc.ca/cwrcdata/https was being used incorrectly

I think it's to do with the assignment of self.placeholderURI

tasks

• [x] Test values assigned to self.placeholderURI
• [x] Update variable
• [ ] Test on subset of files
• [ ] rerun extraction