Avoid decoding multiple times the domain name when it comes in
sequence. This happens when a given domain label either has multiple
entries in its record set or when it's a CNAME (or both), such as in:
;; ANSWER SECTION:
cname-cname.test.qt-project.org. 3600 IN CNAME cname.test.qt-project.org.
cname.test.qt-project.org. 1614 IN CNAME multi.test.qt-project.org.
multi.test.qt-project.org. 1614 IN A 198.51.100.2
multi.test.qt-project.org. 1614 IN A 198.51.100.3
multi.test.qt-project.org. 1614 IN A 198.51.100.1
Label targets from other records such as MX and SRV usually do show up
again, in the Additional section, but the chance that they are
sequential isn't very good, so we don't cache those.
;; ANSWER SECTION:
mx-multi.test.qt-project.org. 3354 IN MX 10 multi.test.qt-project.org.
mx-multi.test.qt-project.org. 3354 IN MX 20 a-single.test.qt-project.org.
;; ADDITIONAL SECTION:
multi.test.qt-project.org. 1145 IN A 198.51.100.3
multi.test.qt-project.org. 1145 IN A 198.51.100.1
multi.test.qt-project.org. 1145 IN A 198.51.100.2
a-single.test.qt-project.org. 3364 IN A 192.0.2.1
Change-Id: I5f7f427ded124479baa6fffd175f5cf88939ee73
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
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