Fix bug in InventoryCollection#find_by with non-default ref

[cben]

Small followup to #15447.
The ref was not being passed to find(), so the id was looked up in wrong hash, most likely resulting in nil.
(lazy_find_by(...) with same params worked.)
At this point, no code was affected (containers graph refresh is only use of secondary refs, but only used lazy_find_by; I stumbled on this when debugging interactively...).

@miq-bot add-label bug

@agrare @Ladas Please review. (This could be a good time to ask me to add tests ;-))

[miq-bot]

Checked commit cben@1359023 with ruby 2.2.6, rubocop 0.47.1, and haml-lint 0.20.0
1 file checked, 0 offenses detected
Everything looks fine. 👍

[Ladas]

@cben looks great 👍

yeah, the specs would be nice, but we can wait till we finish the secondary indexes(db loading, to_yaml, from_yaml, etc.). Then we should test also the targeted approach.

So, I am fine with complex tests a bit later, rather than small one now. :-) @agrare ?

[agrare]

Yeah this is a small enough fix I'm good with getting it in now