[BUG] Alert export errors prevent proper processing of events in eventengine

[lunkwill42]

Describe the bug
We are seeing errors in eventengine.log that indicate various errors in the alert export subsystem (mostly problems with actually serializing the alerts to JSON for output to the stream). It seems these errors stop further processing of the event in question by eventengine, meaning events aren't processed properly.

This only appears to apply if an export script is actually configured in eventengine.conf.

Expected behavior
Export of alerts should only be considered a side-effect of the processing of an event. Errors in this side effect should never prevent the event engine from proceeding with the internal processing of events.

Event engine should log these errors (so they can be tracked down), but ultimately ignore them and move on.

Environment (please complete the following information):

• OS on the NAV server: Debian 10
• NAV version installed: 5.1.0
• Method of installation: from Debian package