Skip a Null GraphQL Node in pr_review.py reviewer_nodes Instead of Crashing wait #3392

Problem

scripts/pr_review.py wait can crash with a traceback when the pull request's comments connection returns a null entry in nodes. reviewer_nodes() calls n.get("author") on every node, so a None node raises:

File "scripts/pr_review.py", in answered_outside_review
    comments = reviewer_nodes(pr, "comments")
File "scripts/pr_review.py", in reviewer_nodes
    if (n.get("author") or {}).get("login") == login
AttributeError: 'NoneType' object has no attribute 'get'

The wait exits 1 with that traceback rather than with one of its documented outcomes, so a driver reads it as neither "met", "pending", nor a named failure.

When it was seen

It came from the first wait run against a freshly opened pull request, seconds after attest posted its comment and a third-party review bot posted its own. A read of the same connection a minute later returned only non-null nodes, and the identical wait run then completed normally. So the null entry looks transient, consistent with GraphQL returning null for a list item it could not resolve at read time (with a matching entry in errors).

Reproduce

Feed reviewer_nodes() a payload whose comments.nodes holds a None, for example {"comments": {"nodes": [None, {"author": {"login": "copilot-pull-request-reviewer"}}]}}. It raises the same AttributeError.

Done when

• reviewer_nodes(), and any sibling that iterates a GraphQL nodes list the same way, skips or reports a null entry rather than raising.
• Whether a null node should make the read count as blind, the way window_blind treats an untrustworthy window, is decided rather than left to the crash.
• A unit test covers a nodes list holding None.