Skip generating recs for missing users from test set (#525)
Skip generating recs for missing users from test set (#525)

During evaluation, don't generate recommendations for users that
don't have any withheld items in the test set. Previously
we skipped  calculating the eval metrics for these users after generating
their recommendatiosn - which caused unnecessary work.

This moves the code to filter out users without any items in the test set
to before we generate recommendations for them,
benfred/implicit,benfred/implicit,benfred/implicit