Events: Fix registering of monitoreditem callbacks
Events: Fix registering of monitoreditem callbacks

Thanks to Tino Bischoff for finding the root-cause

Co-authored-by: Tino Bischoff <da05ff565105bf0d8c4e081e24826ba7a88a1795@iosb.fraunhofer.de>

JGrothoff/open62541,StalderT/open62541,JGrothoff/open62541,jpfr/open62541,open62541/open62541,StalderT/open62541,open62541/open62541,JGrothoff/open62541,open62541/open62541,jpfr/open62541,jpfr/open62541,JGrothoff/open62541,open62541/open62541,StalderT/open62541,StalderT/open62541,jpfr/open62541