Always return a slice from a MultiQuerySet if possible.
Always return a slice from a MultiQuerySet if possible.

Previously: if you tried to take a slice of a MQS and there weren't enough items
to fill it, *nothing* would be returned.  This is not how Python/Django slicing
works, and it was causing problems in the pagination.

For: https://unisubs.sifterapp.com/projects/12298/issues/444976/comments

pculture/unisubs,ujdhesa/unisubs,wevoice/wesub,ujdhesa/unisubs,ReachingOut/unisubs,norayr/unisubs,eloquence/unisubs,eloquence/unisubs,pculture/unisubs,ujdhesa/unisubs,ReachingOut/unisubs,ofer43211/unisubs,ofer43211/unisubs,wevoice/wesub,ofer43211/unisubs,eloquence/unisubs,ujdhesa/unisubs,ReachingOut/unisubs,norayr/unisubs,pculture/unisubs,eloquence/unisubs,ReachingOut/unisubs,norayr/unisubs,ofer43211/unisubs,wevoice/wesub,pculture/unisubs,wevoice/wesub,norayr/unisubs