Requesting a running jobs current state over XHR causes 500 error

When requesting a currently running unfinished jobs current state I get the following error: 
Error 500
Undefined array key "end_time"

The problem seems to be, that inside EbackJob::getStatus($jobId)  $job doesn't have an 'end_time' key as long as the job is still running.

This modification solved my Problem:

`'end_time'      => $job['end_time'] ?? null,`

Version: v0.65.1
