If "rndc signing -nsec3param ..." is ran for a zone which has not yet
been loaded or transferred (i.e. its "db" field is NULL), it will be
silently ignored by named despite rndc logging an "nsec3param request
queued" message, which is misleading.  Prevent this by keeping a
per-zone queue of NSEC3PARAM change requests which arrive before a zone
is loaded or transferred and processing that queue once the raw version
of an inline-signed zone becomes available.