Fix CSV export with S3 blobs

2020-10-22T19:43:23,388 ERROR [AbstractComputation] Computation: sortBlob fails last record: sortBlob-01:+0, after retries.
java.lang.NullPointerException: null
	at java.io.FileInputStream.<init>(FileInputStream.java:130) ~[?:1.8.0_101]
	at com.google.code.externalsorting.ExternalSort.sortInBatch(ExternalSort.java:793) ~[externalsortinginjava-0.2.5.jar:?]
	at com.google.code.externalsorting.ExternalSort.sortInBatch(ExternalSort.java:737) ~[externalsortinginjava-0.2.5.jar:?]
	at com.google.code.externalsorting.ExternalSort.sortInBatch(ExternalSort.java:687) ~[externalsortinginjava-0.2.5.jar:?]
	at com.google.code.externalsorting.ExternalSort.sortInBatch(ExternalSort.java:670) ~[externalsortinginjava-0.2.5.jar:?]
	at com.google.code.externalsorting.ExternalSort.sortInBatch(ExternalSort.java:655) ~[externalsortinginjava-0.2.5.jar:?]
	at com.google.code.externalsorting.ExternalSort.sort(ExternalSort.java:433) ~[externalsortinginjava-0.2.5.jar:?]
	at org.nuxeo.ecm.core.bulk.action.computation.SortBlob.sort(SortBlob.java:106) ~[nuxeo-core-bulk-10.10-HF33.jar:?]
	at org.nuxeo.ecm.core.bulk.action.computation.SortBlob.processRecord(SortBlob.java:74) ~[nuxeo-core-bulk-10.10-HF33.jar:?]
	at org.nuxeo.lib.stream.computation.log.ComputationRunner.lambda$processRecordWithRetry$10(ComputationRunner.java:375) ~[nuxeo-stream-10.10-HF30.jar:?]
	at net.jodah.failsafe.Functions$10.call(Functions.java:252) ~[failsafe-1.1.0.jar:1.1.0]
	at net.jodah.failsafe.SyncFailsafe.call(SyncFailsafe.java:145) [failsafe-1.1.0.jar:1.1.0]
	at net.jodah.failsafe.SyncFailsafe.run(SyncFailsafe.java:81) [failsafe-1.1.0.jar:1.1.0]
	at org.nuxeo.lib.stream.computation.log.ComputationRunner.processRecordWithRetry(ComputationRunner.java:375) [nuxeo-stream-10.10-HF30.jar:?]
	at org.nuxeo.lib.stream.computation.log.ComputationRunner.processRecord(ComputationRunner.java:358) [nuxeo-stream-10.10-HF30.jar:?]
	at org.nuxeo.lib.stream.computation.log.ComputationRunner.processLoop(ComputationRunner.java:248) [nuxeo-stream-10.10-HF30.jar:?]
	at org.nuxeo.lib.stream.computation.log.ComputationRunner.run(ComputationRunner.java:185) [nuxeo-stream-10.10-HF30.jar:?]
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_101]
	at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_101]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [?:1.8.0_101]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [?:1.8.0_101]
	at java.lang.Thread.run(Thread.java:745) [?:1.8.0_101]