improve inputdata checks

[mahf708]

Per @rljacob: We got this advice “If you don’t need to download it, you can send a HTTP HEAD request, like these examples https://gist.github.com/dehowell/884204 or this https://stackoverflow.com/a/35881430
That would be easier on the webserver and should run faster.”

[bartgol]

Out of curiosity: does this address the 403 Forbidden error as well?

[rljacob]

No. Those were from blocks put in at the web server. This is just good practice going forward.

[mahf708]

Yeah, just to lessen the pressure on the server