Use dns_name_copy() to hold the copied name
In tkey.c, dns_name_clone() was being used to copy the source name into dns_fixedname_t structure. However the dns_name_clone() just makes the target->ndata = source->ndata and when source->ndata is gone, so is target->ndata.
The function that needs to be used here is dns_name_copynf() that copies the source->ndata to target->ndata buffer.
As a side note - no memory was lost, because the ndata buffer used in the dns_fixedname_t is internal to the structure and freed when the dns_fixedname_t is freed regardless of the .ndata contents.
Closes #2713 (closed)