Fix cudf::repeat logic when count is zero

[davidwendt]

Description

Fixes logic in cudf::repeat to check for count==0 before using it to check for possible out-of-bounds output size result.
Added a specific gtest for this as well.

Closes #13458

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[bdice]

I would support this fix going into 23.06. It's very low risk and fixes a crash.

[jlowe]

I verified this fixes the crashes we saw in our Spark integration test. Thanks for the quick turnaround, @davidwendt!

Note that we would like to see this in 23.06 to unblock our release pipelines there.

[bdice]

Oops, I made a mistake (and fixed it). I changed the target branch to 23.06 and reverted it. We do need to rebase this over branch-23.06. Luckily it's only a single commit so this is not too tough. @davidwendt Can you rebase and change the target? cc: @GregoryKimball since this fix is needed during freeze.

[davidwendt]

My git foo is weak so I'll need help rebasing this PR.

[bdice]

@davidwendt the rebase looks good to me. I think we’ll need an admin merge once CI passes.