Handle error when Origin header value is not IRI

[csarven]

Server breaks when Origin header value is not an IRI. See:

node-solid-server/lib/acl-checker.js

Line 31 in 958a6ef

this.agentOrigin=options.strictOrigin&&options.agentOrigin ? rdf.sym(options.agentOrigin) : null

calling rdf.sym where an Error is thrown but it is not caught.

Following examples typically return 200:

$ curl -i https://example.org/ $ curl -iH 'Origin: https://example.net' https://example.org/

Following examples breaks the script (bin/solid.js). 500 returned.

$ curl -iH 'Origin: null' https://example.org/ $ curl -iH 'Origin: breaking bad' https://example.org/

There may be a better way to fix this issue than what's in this PR but I'll leave it in the hands of folks that can do better.

[ewingson]

happy to review.
Sarven has tested it as in https://app.element.io/#/room/!YCVoUIVohPTofEksKL:matrix.org/$hkj5YAplQrKLQaAxt6ZKCR4vbvUU94Y4lpwH0hm4ugg

LGTM