[9.20] fix: usr: Fix assertion failure when dumping recursing clients

Previously, if a new counter was added to the hashtable
while dumping recursing clients via the `rndc recursing`
command, and `fetches-per-zone` was enabled, an assertion
failure could occur. This has been fixed.

Closes #5200

Backport of MR !10164

Merge branch 'backport-5200-destroy-iterator-inside-the-rwlock-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!10168

lib/dns/resolver.c

@@ -11087,8 +11087,8 @@ dns_resolver_dumpquota(dns_resolver_t *res, isc_buffer_t **buf) {
 	}
 
 cleanup:
-	RWUNLOCK(&res->counters_lock, isc_rwlocktype_read);
 	isc_hashmap_iter_destroy(&it);
+	RWUNLOCK(&res->counters_lock, isc_rwlocktype_read);
 	return result;
 }