Werk #11902: Fix crash in Rittal CMC III temperature check

Component	Checks & agents
Title	Fix crash in Rittal CMC III temperature check
Date	Feb 1, 2021
Level	Trivial Change
Class	Bug Fix
Compatibility	Incompatible - Manual interaction might be required
Checkmk versions & editions	2.1.0b1 Checkmk Community, Checkmk Pro, Checkmk Ultimate MT 2.0.0p16 Checkmk Community, Checkmk Pro, Checkmk Ultimate MT

Some entries (such as the ones for the blue LED) do not report their temperatures. However, the missing temperature would crash the check.

Note: The device must be rediscovered.

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