Werk #12705: Fix "Checker and fetcher mismatch" for SNMP devices that cannot be resolved

The service Check_MK Discovery could produce a crash report with the error "Checker and fetcher mismatch" if the address of an SNMP host cannot be resolved. Alternatively, the service would be OK although the host was not checked.

Now, the service for the unreachable host will fail consistently (CRIT) with the error: "Host has no IP address configured".

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