Werk #8533: Fixed possible mixup of check results resulted by a timeout in a check helper

When the check of a host resulted in a timeout, it could happen that the check helper which handled the time out was left in an unintended state making the next check timeout too early. This could result in the check helper / core communication being mixed up. As result one host could get the check results of another reported which mostly lead to an error message "ignoring check result for [host] / [service]: no such service".

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