Werk #10249: Fix type error when listing alert handler rules

Component	Setup
Title	Fix type error when listing alert handler rules
Date	Oct 4, 2019
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	2.0.0i1 Checkmk Enterprise (CEE), Checkmk MSP (CME) 1.6.0p5 Checkmk Enterprise (CEE), Checkmk MSP (CME)

A "TypeError" exception could occur after creating alert handler rules while trying to render the alert handler rule list.

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