Fix integer background job id type error

[ChristophWurst]

Fixes

{"reqId":"EHhZ5rL76Y4IGKW5rV51","level":3,"time":"2019-01-15T13:35:17+00:00","remoteAddr":"","user":"--","app":"cron","method":"","url":"--","message":{"Exception":"TypeError","Message":"Return value of OCP\\BackgroundJob\\Job::getId() must be of the type int, string returned","Code":0,"Trace":[{"file":"\/home\/christoph\/workspace\/nextcloud\/cron.php","line":118,"function":"getId","class":"OCP\\BackgroundJob\\Job","type":"->","args":[]}],"File":"\/home\/christoph\/workspace\/nextcloud\/lib\/public\/BackgroundJob\/Job.php","Line":117,"CustomMessage":"--"},"userAgent":"--","version":"16.0.0.0"}

That fails because of

server/lib/public/BackgroundJob/Job.php

Line 116 in 99dea46

finalpublicfunctiongetId(): int {

. I now just assumed they are always int, hence the type cast.

[rullzer]

backport I assume?

[rullzer]

/backport to stable15

[backportbot-nextcloud]

backport to stable15 in #13609