Fix bug notifier for issues with no body text

[hugovk]

Possible fix for https://github.com/python/cpython/actions/runs/22773539894/job/66060786931

GET /repos/python/cpython/issues/145599 - 200 in 266ms
TypeError: Cannot read properties of null (reading 'substring')
    at eval (eval at callAsyncFunction (/home/runner/work/_actions/actions/github-script/v8/dist/index.js:36187:16), <anonymous>:24:30)
    at process.processTicksAndRejections (node:internal/process/task_queues:103:5)
Error: Unhandled error: TypeError: Cannot read properties of null (reading 'substring')

The issue #145599 was created with no body, and we should always have at least a brief description. But something like this should let the notifier still process it if it happens again.

[webknjaz]

Looks right