Fix setting job platforms when props are empty
There is a bug here when the platform_requirements dict is empty. The line
select(PlatformEntry.key, PlatformEntry.value).where(or_(*conditions))
Becomes:
select(PlatformEntry.key, PlatformEntry.value).where(or_(*[]))
Which is the same as
select(PlatformEntry.key, PlatformEntry.value)
This leads to a job with no platform properties being assigned them all...
Quick fix is to short circuit on empty values.