fix: dev: Fix the foundname vs dcname madness in qpcache_findzonecut()

The qpcache_findzonecut() accepts two "foundnames": 'foundname' and
'dcname' could be NULL.  Originally, when 'dcname' would be NULL, the
'dcname' would be set to 'foundname' which basically means that we were
copying the .ndata over itself for no apparent reason.

Merge branch 'ondrej/refactor-qpcache_findzonecut' into 'main'

See merge request isc-projects/bind9!10049