Ignore zero sized chunks in auto_chunks

[jasonkena]

• Closes #xxxx
• Tests added / passed
• Passes pre-commit run --all-files

When an array is interspersed with empty chunks, the zero-valued chunks skew the median; this accounts for that while maintaining original behavior if the array only contains empty chunks.

Test cases are yet to be added.

[GPUtester]

Can one of the admins verify this patch?

Admins can comment ok to test to allow this one PR to run or add to allowlist to allow all future PRs from the same author to run.

[pavithraes]

ok to test

[ncclementi]

@jasonkena Do you have a reproducible example that we can run to see how this behaved before and after the change?
Similarly, would you mind adding a test for this new behavior? I see we have two path codes (if/else) and we should cover both of them.