incorrect application of join condition when parent triples map and child triples map are identical

[elsdvlee]

Example:

• mapping file: test-parentStation-csv01.yml.txt converted to test-parentStation-csv01.ttl.txt
• source file: STOPS.csv
• output: test-parentStation-csv01.nt.txt

Only one parent station triple is generated:
<http://transport.linkeddata.es/madrid/metro/stops/0000000000000000003t> <http://vocab.gtfs.org/terms#parentStation> <http://transport.linkeddata.es/madrid/metro/stops/0000000000000000003t>.

RML Mapper looks only if rr:parent is equal to rr:child on the one row of the iterator, not in the complete source file.

Correct output according to morph-kgc (using the same mapping file as above mentioned) is: test-parentStation-csv01-morphkgc.nt.txt.
Same correct output can be generated by using an adapted mapping file in RML Mapper, test-parentStation-csv01-bis.yml.txt: adding a second triples map.

(I have added the suffix .txt after each file to be able to upload them in this issue.)