Fix override of slot build id to accept 0
When calling lbn-checkout
on a slot configuration that has a non-null build_id
(e.g. to reproduce a given nightly build), the git checkout method overrides the tag in the special lhcb-nightlies repository with the new one.
The only practical way to avoid it is to set to 0 the slot build_id
, but the command line option --slot-build-id
overrides the configuration one only if not null.