Werk #7209: Don't crash upon missing Swarm Info

Component	Checks & agents
Title	Don't crash upon missing Swarm Info
Date	Mar 7, 2019
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	1.5.0p13 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk MSP (CME)

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