Bug fix: replace_nulls_policy functor not returning correct indices for gathermap

[isVoid]

Closes #8673

This PR fixes a bug in the functor for replace_nulls(replace_policy). The current functor assumes that the second element of the pair is discarded and is arbitrarily returned true. This breaks the associative constraints for inclusive_scan functors.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (branch-21.08@8aaf8e6). Click here to learn what that means.
The diff coverage is n/a.

❗ Current head 14596f6 differs from pull request most recent head d320e1f. Consider uploading reports for the commit d320e1f to get more accurate results

@@               Coverage Diff               @@
##             branch-21.08    #8699   +/-   ##
===============================================
  Coverage                ?   10.62%           
===============================================
  Files                   ?      109           
  Lines                   ?    18291           
  Branches                ?        0           
===============================================
  Hits                    ?     1943           
  Misses                  ?    16348           
  Partials                ?        0           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 8aaf8e6...d320e1f. Read the comment docs.

[galipremsagar]

Pytest approval

[galipremsagar]

@gpucibot merge