Fix dangling references to outdated views after reconfig

Fix dangling references to outdated views after reconfig

This commit fix a leak which was happening every time an inline-signed
zone was added to the configuration, followed by a rndc reconfig.

During the reconfig process, the secure version of every inline-signed
zone was "moved" to a new view upon a reconfig and it "took the raw
version along", but only once the secure version was freed (at shutdown)
was prev_view for the raw version detached from, causing the old view to
be released as well.

This caused dangling references to be kept for the previous view, thus
keeping all resources used by that view in memory.