4010. [cleanup] Clear the prefetchable state when initiating a prefetch.

[RT #37399]

lib/dns/ncache.c

@@ -503,6 +503,7 @@ static dns_rdatasetmethods_t rdataset_methods = {
 	NULL,
 	NULL,
 	rdataset_settrust,
+	NULL,
 	NULL
 };