lightningd: have sign_last_tx populate the input amounts.

With this change, all bitcoin_tx we send across the wire have
their inputs_amounts populated.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/peer_control.c

@@ -184,7 +184,13 @@ static void sign_last_tx(struct channel *channel)
 	u8 *msg, **witness;
 
 	assert(!channel->last_tx->wtx->inputs[0].witness);
-
+	/* Attach input amount, to complete transaction for marshaling */
+	if (!channel->last_tx->input_amounts[0]) {
+		channel->last_tx->input_amounts[0]
+			= tal_dup(channel->last_tx->input_amounts,
+				  struct amount_sat,
+				  &channel->funding);
+	}
 	msg = towire_hsm_sign_commitment_tx(tmpctx,
 					    &channel->peer->id,
 					    channel->dbid,