Handle invalid /$/download and /$/stream with a 404 (#1676)

## Issue
- When `/$/download/:claimname/:claimId` is invalid, it results in a bad redirect loop that keeps requesting the same thing. Eventually it stops, though.
- When `/$/stream/:claimname/:claimId` is invalid, it results in a 302 page that simply says `Redirecting to .`, and is increasing in count in the search console.

## Fix
Return a 404 not found for these.

web/src/routes.js

@@ -42,13 +42,17 @@ router.get(`/$/api/content/v2/get`, async (ctx) => getHomepage(ctx, 2));
 
 router.get(`/$/download/:claimName/:claimId`, async (ctx) => {
   const streamUrl = await getStreamUrl(ctx);
+  if (streamUrl) {
     const downloadUrl = `${streamUrl}?download=1`;
     ctx.redirect(downloadUrl);
+  }
 });
 
 router.get(`/$/stream/:claimName/:claimId`, async (ctx) => {
   const streamUrl = await getStreamUrl(ctx);
+  if (streamUrl) {
     ctx.redirect(streamUrl);
+  }
 });
 
 router.get(`/$/activate`, async (ctx) => {