Use correct HRMP path for parachain sibling (#366)

cumulus/pallets/xcm-handler/src/lib.rs

@@ -184,7 +184,8 @@ impl<T: Config> SendXcm for Module<T> {
 				Ok(())
 			}
 			// An HRMP message for a sibling parachain.
-			Some(Junction::Parachain { id }) => {
+			Some(Junction::Parent) if dest.len() == 2 => {
+				if let Some(Junction::Parachain { id }) = dest.at(1) {
 					let data = msg.encode();
 					let hash = T::Hashing::hash(&data);
 					let message = OutboundHrmpMessage {
@@ -195,6 +196,9 @@ impl<T: Config> SendXcm for Module<T> {
 						.map_err(|_| XcmError::CannotReachDestination)?;
 					Self::deposit_event(RawEvent::HrmpMessageSent(hash));
 					Ok(())
+				} else {
+					Err(XcmError::UnhandledXcmMessage)
+				}
 			}
 			_ => {
 				/* TODO: Handle other cases, like downward message */