share: raw path to directory leads to internal server error

[haraldschilly]

When trying to open https://cocalc.com/share/raw/8b892baf91f98d0cf6172b872c8ad6694d0f7204/PythonDataScienceHandbook I get an internal server error.

I didn't investigate in detail, but I think it's a directory and that can't be handled.

1. The server should just reply that this is not supported
2. There must be somewhere a "raw" link, which should be removed

Error: EISDIR, read
    at SendStream.ondirectory (/cocalc/lib/node_modules/@cocalc/hub/node_modules/express/lib/response.js:1062:15)
    at SendStream.emit (node:events:513:28)
    at SendStream.redirect (/cocalc/lib/node_modules/@cocalc/hub/node_modules/send/index.js:475:10)
    at onstat (/cocalc/lib/node_modules/@cocalc/hub/node_modules/send/index.js:723:41)
    at FSReqCallback.oncomplete (node:fs:207:5)