🐛 Fixed not-equal filters when combined with others

when applying two or more "unsubscribed from newsletter" filters, NQL would skip the entire filter
the root cause of that bug is a recent optimisaton around combining multiple "not equal" filters into a single "not in" array
with this fix, we apply a few safeguards to the optimisation, so that we can fallback safely when the optimisation is not applicable

TryGhost / NQL