Use source and destination iterators in loop
Use source and destination iterators in loop

Rewrite usage of source and destination iterators in the `while`-loop to
not rely on indexing, but merely on advancing the existing iterators'
positions.

DudLab/rank_filter,jakirkham/rank_filter,nanshe-org/rank_filter,DudLab/rank_filter,DudLab/rank_filter,jakirkham/rank_filter,jakirkham/rank_filter,nanshe-org/rank_filter,nanshe-org/rank_filter