routing: fix mc blinded path behaviour. #16875

Job	Run time
RPC and mobile compilation check	6m 58s
check commits	5m 6s
sample configuration check	5m 34s
cross compilation	20m 57s
lint code	7m 59s
Sqlc check	4m 8s
run ubuntu itests (btcd, backend=btcd cover=1)	14m 2s
run unit tests (btcd unit-cover)	6m 19s
run ubuntu itests (bitcoind, backend=bitcoind cover=1)	19m 43s
run unit tests (unit tags="kvdb_etcd")	20m 54s
check pinned dependencies (google.golang.org/grpc v1.59.0)	3s
run ubuntu itests (bitcoind-notxindex, backend="bitcoind notxindex")	17m 4s
run unit tests (unit tags="kvdb_postgres")	19m 49s
check pinned dependencies (github.com/golang/protobuf v1.5.3)	4s
run ubuntu itests (bitcoind-rpcpolling, backend="bitcoind rpcpolling" cover=1)	15m 15s
run unit tests (unit tags="kvdb_sqlite")	18m 44s
run ubuntu itests (bitcoind-etcd, backend=bitcoind dbbackend=etcd)	20m 37s
run unit tests (btcd unit-race)	20m 57s
run macOS itest	20m 58s
run ubuntu itests (bitcoind-postgres, backend=bitcoind dbbackend=postgres)	16m 41s
run unit tests (unit-module)	1m 6s
run ubuntu itests (bitcoind-sqlite, backend=bitcoind dbbackend=sqlite)	14m 36s
run ubuntu itests (bitcoind-postgres-nativesql, backend=bitcoind dbbackend=postgres nativesql=true)	15m 43s
check release notes updated	2s
run windows itest	7m 23s
run ubuntu itests (bitcoind-sqlite-nativesql, backend=bitcoind dbbackend=sqlite nativesql=true)	13m 59s
run ubuntu itests (neutrino, backend=neutrino cover=1)	13m 54s
finish	4s
	5h 28m 39s

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