Werk #13617: Fix crash during parsing of enviromux section

Component	Checks & agents
Title	Fix crash during parsing of enviromux section
Date	Feb 23, 2022
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	2.2.0b1 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk Cloud (CCE), Checkmk MSP (CME) 2.1.0b1 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk MSP (CME) 2.0.0p21 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk MSP (CME)

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