Don't set startCursor in relayStylePagination when only one cursor is present

[sdeleur-sc]

In relayStylePagination, the startCursor and endCursor are set based on cursors under the edges if the information is not present under the pageInfo. This works well when both of the cursors are defined under the nodes. However, if only a single cursor is present, both of the fields get populated with the same cursor, causing startCursor and endCursor to have the same value.

This causes an issue on subsequent merge operation because the startCursor gets written to the first edge here, causing duplicate edges to have the same cursor

The expected behavior here is for only the endCursor to be populated and for startCursor to remain empty when only a single cursor is present under the edges.

Checklist:

• If this PR contains changes to the library itself (not necessary for e.g. docs updates), please include a changeset (see CONTRIBUTING.md)
• If this PR is a new feature, please reference an issue where a consensus about the design was reached (not necessary for small changes)
• Make sure all of the significant new logic is covered by tests

[apollo-cla]

@sdeleur-sc: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Apollo Contributor License Agreement here: https://contribute.apollographql.com/

[netlify]

👷 Deploy request for apollo-client-docs pending review.

Visit the deploys page to approve it

Name	Link
🔨 Latest commit	9090b82

[changeset-bot]

🦋 Changeset detected

Latest commit: 9090b82

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@apollo/client	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[jerelmiller]

🔥 🔥 This looks great to me and the logic is sound. Great to see you were able to make this change in a way that preserved all the existing logic.

Thanks so much for the contribution!

[jerelmiller]

/release:pr

[github-actions]

Please add a changeset via npx changeset before attempting a snapshot release.