Load time is not updated for unchanged inline-signed zones

When a zone file of an inline-signed zone has a modification time newer than the last rndc reload time, but its contents have not actually changed since the last rndc reload, named queues a redundant zone reload: rndc reload <zonename> logs zone reload queued and named produces (harmless, yet confusing) log messages like this one:

zone example/IN (unsigned): ixfr-from-differences: unchanged

The problem here is that the code branch logging ixfr-from-differences: unchanged does not update zone->loadtime, which leads named to believe that the zone has been changed since load time upon every subsequent rndc reload (until the situation is rectified e.g. by actually updating the contents of the unsigned zone, which causes zone_postload() to be called in order to i.a. update zone->loadtime).