fix: nil pointer when search fails #151

Job	Run time
ci-lint	22s
setup-params	4s
build-all	3m 45s
docs-check	2m 34s
cbor-check	1m 19s
gen-check	2m 45s
gofmt	46s
lint	3m 41s
mod-tidy-check	50s
lid-docker-compose	1m 15s
test (test-itest-dummydeal_offline, ./itests/dummydeal_offline_test.go)	2m 9s
test (test-itest-dummydeal, ./itests/dummydeal_test.go)	2m 28s
test (test-graphsync_identity_cid, ./itests/graphsync_identity_cid_test.go)	2m 41s
test (test-itest-retrieval, ./itests/graphsync_retrieval_test.go)	2m 28s
test (test-itest-direct_deal, ./itests/ddo_test.go)	2m 18s
test (test-all, `go list ./... \| grep -v boost/db \| grep -v boost/storagemarket \| grep -v boost/i...	3m 17s
test (test-itest-data-segment-index, ./itests/data_segment_index_retrieval_test.go)	2m 52s
test (test-itest-ipni, ./itests/ipni_publish_test.go)	1m 54s
test (test-itest-multiminer-graphsync, ./itests/multiminer_retrieval_graphsync_test.go)	2m 0s
test (test-booster-http, ./cmd/booster-http)	5m 48s
test (test-booster-bitswap, ./cmd/booster-bitswap)	2m 18s
test (test-itest-lid-cleanup, ./itests/lid_cleanup_test.go)	3m 32s
test (test-provider, ./storagemarket)	2m 10s
test (test-sql-db, ./db)	1m 12s
	54m 28s

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