Werk #16376: DCD: Not respecting "Validity of missing data" setting

This fixes disappearing hosts in case of temporarily missing data around the time when a cleanup background job is run (around midnight).

In case a piggybacked host temporarily did not receive any data while the background (cron) job cmk --cleanup-piggyback was executed, a subsequent run of the DCD would not respect the "Validity of missing data" setting, wrongly removing the affected host from the monitoring configuration.

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