Add some safety to the proposals script (#1368)

* Add some safety to the proposals script

for if github's api explodes, forgets the header, or we are rate limited or something.

* changelog

changelogs/internal/newsfragments/1368.clarification

@@ -0,0 +1 @@
+Improve safety of the proposals retrieval script in the event of failure.

scripts/proposals.js

@@ -100,7 +100,7 @@ async function getIssues() {
     const issuesForPage = await response.json();
     issues = issues.concat(issuesForPage);
     const linkHeader = response.headers.get("link");
-    pageLink = getNextLink(linkHeader);
+    pageLink = !!linkHeader ? getNextLink(linkHeader) : null;
   }
 }