fix: Job result returns proper page when start_index and page_size are not null

[manucalop]

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Fixes #1569 🦕

[google-cla]

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[manucalop]

CLA is fixed now

[manucalop]

Hi! Any updates on this? Could someone rerun the CLA job? I've already updated my status

[chalmerlowe]

Thanks for submitting a PR.

I took a quick look.

• Gonna run our CI/CD checks on this.
• My first thought is that because we are adding a couple code paths coverage is likely to fail.

[manucalop]

Hi! Any update on this? Anything I can do to help?

[chalmerlowe]

@manucalop

I will do my best to take a look at this PR today. I appreciate your time and effort to help out the project.

[chalmerlowe]

I got derailed yesterday. I am looking at a number of issues related to page_size handling by the bigquery library, so this is on my radar, I just didn't have a change to look closely.

I do see that coverage was not happy with this change so we will potentially need to consider the addition of a test or two to ensure that we fully exercise all the code paths around and through this code change.

Name                                Stmts   Miss Branch BrPart  Cover   Missing
-------------------------------------------------------------------------------
google/cloud/bigquery/job/query.py    801      1    170      1    99%   1551