Missing catch in ice.js

[cjmyers]

There are many places in this file missing catch statements and some are causing recurrent failures:

getIceSequence: ERROR TypeError: Cannot read property 'childNodes' of undefined : https://public-registry.jbei.org/rest/file/8922/sequence/sbol2
(node:14902) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'childNodes' of undefined
at RdfLibParser.parse (/home/deploy/synbiohub_dev/node_modules/rdf-parser-rdfxml/index.js:226:29)
at /home/deploy/synbiohub_dev/node_modules/rdf-parser-rdfxml/index.js:624:31
at new Promise ()
at RdfXmlParser.process (/home/deploy/synbiohub_dev/node_modules/rdf-parser-rdfxml/index.js:577:10)
at /home/deploy/synbiohub_dev/node_modules/rdf-parser-abstract/index.js:19:10
at new Promise ()
at RdfXmlParser.AbstractParser.parse (/home/deploy/synbiohub_dev/node_modules/rdf-parser-abstract/index.js:18:10)
at loadNextSource (/home/deploy/synbiohub_dev/node_modules/sboljs/lib/load/rdf/loadRDF.js:79:16)
at load (/home/deploy/synbiohub_dev/node_modules/sboljs/lib/load/rdf/loadRDF.js:75:5)
at SBOLDocument.loadRDF (/home/deploy/synbiohub_dev/node_modules/sboljs/lib/SBOLDocument.js:842:9)
at Function.loadRDF (/home/deploy/synbiohub_dev/node_modules/sboljs/lib/SBOLDocument.js:807:22)
at Request.request [as _callback] (/home/deploy/synbiohub_dev/lib/ice.js:293:26)
at Request.self.callback (/home/deploy/synbiohub_dev/node_modules/request/request.js:185:22)
at emitTwo (events.js:126:13)
at Request.emit (events.js:214:7)
at Request. (/home/deploy/synbiohub_dev/node_modules/request/request.js:1161:10)
(node:14902) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 17)