4377. [bug] Don't reuse zero TTL responses beyond the current

client set (excludes ANY/SIG/RRSIG queries).
                        [RT #42142]

bin/tests/system/zero/ns1/root.db

@@ -22,3 +22,5 @@ example. NS ns2.example.
 ns2.example. A 10.53.0.2
 example. NS ns4.example.
 ns4.example. A 10.53.0.4
+increment. NS incrementns.
+incrementns A 10.53.0.5