Return only Some(block_hash) in CM rel. txids

As of now the `Confirm::get_relevant_txids()` docs state that it won't
return any transactions for which we hadn't previously seen a
confirmation. To align its functionality a bit more with the docs, at
least for `ChannelManager`, we only return values for which we had
registered a confirmation block hash before.

Author: tnull

lightning/src/ln/channelmanager.rs

@@ -5786,8 +5786,8 @@ where
 			let mut peer_state_lock = peer_state_mutex.lock().unwrap();
 			let peer_state = &mut *peer_state_lock;
 			for chan in peer_state.channel_by_id.values() {
-				if let (Some(funding_txo), block_hash) = (chan.get_funding_txo(), chan.get_funding_tx_confirmed_in()) {
-					res.push((funding_txo.txid, block_hash));
+				if let (Some(funding_txo), Some(block_hash)) = (chan.get_funding_txo(), chan.get_funding_tx_confirmed_in()) {
+					res.push((funding_txo.txid, Some(block_hash)));
 				}
 			}
 		}