Sometimes operates on issues/PRs that are already closed

[JamesMGreene]

For the "Stale" Probot App, we have received a fair number of reports ([1], [2], [2]) that the app was unexpected operating on issues and PRs that had already been closed. Given that our query to the Issue Search API explicitly included the is:open condition, we determined that this appears to be a more recently introduced bug or shortcoming of the Issue Search API itself -- likely due to outdated indexing.

Luckily, since we are already retrieving the list of issues to be operated on, it was easy enough to add the simple and inexpensive workaround of just checking each issue's state value to verify it was still "open" before processing it.

The same type of workaround should be included in the Stale action as well.

[hross]

thanks for the PR and tests. I'll create a new release from master after a few more fixes go in.