dns_rdatalist_tordataset() and dns_rdatalist_fromrdataset() can not fail
Cleanup dns_rdatalist_tordataset() and dns_rdatalist_fromrdataset() functions by making them return void, because they can not fail.
Cleanup other function that subsequently can not fail.
Closes #3467 (closed)
Edited by Arаm Sаrgsyаn