lnwallet+itest: fix PaymentDescriptor creation for blinded path htlc

This commit fixes the instantiation of the BlindingPoint member of
PaymentDescriptor during the conversion from persisted LogUpdates.
Previously, the blinding point was not set correctly. The test from the
previous commit is also updated to now assert that this behaviour is now
correct.

lnwallet/channel.go

@@ -205,7 +205,7 @@ func PayDescsFromRemoteLogUpdates(chanID lnwire.ShortChannelID, height uint64,
 					Height: height,
 					Index:  uint16(i),
 				},
-				BlindingPoint: pd.BlindingPoint,
+				BlindingPoint: wireMsg.BlindingPoint,
 			}
 			pd.OnionBlob = make([]byte, len(wireMsg.OnionBlob))
 			copy(pd.OnionBlob[:], wireMsg.OnionBlob[:])