APWeb shutsdown if user stops download of jpg through file browser

apweb shuts down if I do the following:

- place a .jpg file on the filesystem
- open the apweb file browser (http://10.0.1.128/filesystem.html) and click on the jpg file
- on the browser press stop or back to abort the file download/viewing
- the image appears but apweb shutsdown and any further attempts to use apweb fail.

By the way, if I restart apweb using, "sudo ./start_apweb.sh" then apweb works again and I see "hearbeat ok" written on the console but if I again click on on another jpg, the "heartbeat ok" messages stop and control is returned to me.

Reproduce the failure through filesystem.html by opening a JPG and pressing stop or back, then inspect the console heartbeat output and restart behavior using start_apweb.sh. Trace the request handling for an aborted image download; done means cancelling the download no longer shuts down APWeb and subsequent file requests continue to work.

Written by the indexing model from the issue text.