Werk #3781: ipmi: made check more robust against incomplete datasets

Component	Checks & agents
Title	ipmi: made check more robust against incomplete datasets
Date	Aug 26, 2016
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	1.4.0i1 Checkmk Community, Checkmk Pro, Checkmk Ultimate MT

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