routing: fix mc blinded path behaviour. #16828

Job	Run time
lint code	3m 26s
cross compilation	3m 28s
check pinned dependencies (google.golang.org/grpc v1.59.0)	6s
check commits	3m 27s
check pinned dependencies (github.com/golang/protobuf v1.5.3)	4s
run macOS itest	3m 32s
check release notes updated	3s
RPC and mobile compilation check	3m 27s
sample configuration check	1m 51s
Sqlc check	2m 42s
run ubuntu itests (btcd, backend=btcd cover=1)	3m 25s
run unit tests (btcd unit-cover)	1m 29s
run ubuntu itests (bitcoind, backend=bitcoind cover=1)	3m 26s
run unit tests (unit tags="kvdb_etcd")	2m 23s
run ubuntu itests (bitcoind-notxindex, backend="bitcoind notxindex")	3m 26s
run windows itest	3m 8s
run unit tests (unit tags="kvdb_postgres")	24s
run ubuntu itests (bitcoind-rpcpolling, backend="bitcoind rpcpolling" cover=1)	3m 25s
run unit tests (unit tags="kvdb_sqlite")	1s
run ubuntu itests (bitcoind-etcd, backend=bitcoind dbbackend=etcd)	3m 27s
run unit tests (btcd unit-race)	3m 17s
run unit tests (unit-module)	1s
run ubuntu itests (bitcoind-postgres, backend=bitcoind dbbackend=postgres)	3m 27s
run ubuntu itests (bitcoind-sqlite, backend=bitcoind dbbackend=sqlite)	3m 25s
run ubuntu itests (bitcoind-postgres-nativesql, backend=bitcoind dbbackend=postgres nativesql=true)	3m 28s
run ubuntu itests (bitcoind-sqlite-nativesql, backend=bitcoind dbbackend=sqlite nativesql=true)	3m 25s
run ubuntu itests (neutrino, backend=neutrino cover=1)	3m 25s
finish	6s
	1h 7m 14s

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