no response in ui when manifest cannot be fetched

[ConorSheehan1]

While going through the iiif workshop on monday, I think I found a bug in the validator.
Submitting a manifest hosted locally using the URL format returns the correct error

https://iiif.io/api/presentation/validator/service/validate?format=json&version=2.0&url=http://127.0.0.1:8887/manifest.json

{"url": "http://127.0.0.1:8887/manifest.json", "okay": 0, "error": "Cannot fetch url"}

but submitting it using the UI, doesn't display any response, but throws an error in the console:

(index):152 Uncaught TypeError: Cannot read property 'length' of undefined
    at Object.handleValidationResponse [as success] ((index):152)
    at i (jquery-2.2.3.min.js:2)
    at Object.fireWith [as resolveWith] (jquery-2.2.3.min.js:2)
    at z (jquery-2.2.3.min.js:4)
    at XMLHttpRequest.<anonymous> (jquery-2.2.3.min.js:4)

The problem seems to be that data.warnings is undefined, so calling length on it throws an error.

presentation-validator/index.html

Line 144 in e620780

if (data.warnings.length){

Maybe errors when fetching the resource could be added to warnings too?