Move holder_commitment_point advancement

Now that validate_commitment_signed encapsulates all funding-specific
checks, move the holder_commitment_point advancement immediately
following the call to it. While there should be any early returns at
that point, it's good to have move it earlier in case of future changes.

Author: jkczyz

lightning/src/ln/channel.rs

@@ -5638,6 +5638,20 @@ impl<SP: Deref> FundedChannel<SP> where
 
 		let commitment_tx_info = self.context.validate_commitment_signed(&self.funding, &self.holder_commitment_point, msg, logger)?;
 
+		if self.holder_commitment_point.advance(&self.context.holder_signer, &self.context.secp_ctx, logger).is_err() {
+			// We only fail to advance our commitment point/number if we're currently
+			// waiting for our signer to unblock and provide a commitment point.
+			// During post-funding channel operation, we only advance our point upon
+			// receiving a commitment_signed, and our counterparty cannot send us
+			// another commitment signed until we've provided a new commitment point
+			// in revoke_and_ack, which requires unblocking our signer and completing
+			// the advance to the next point. This should be unreachable since
+			// a new commitment_signed should fail at our signature checks in
+			// validate_commitment_signed.
+			debug_assert!(false, "We should be ready to advance our commitment point by the time we receive commitment_signed");
+			return Err(ChannelError::close("Failed to advance our commitment point".to_owned()));
+		}
+
 		// Update state now that we've passed all the can-fail calls...
 		let mut need_commitment = false;
 		if let &mut Some((_, ref mut update_state)) = &mut self.context.pending_update_fee {
@@ -5693,18 +5707,6 @@ impl<SP: Deref> FundedChannel<SP> where
 			channel_id: Some(self.context.channel_id()),
 		};
 
-		if self.holder_commitment_point.advance(&self.context.holder_signer, &self.context.secp_ctx, logger).is_err() {
-			// We only fail to advance our commitment point/number if we're currently
-			// waiting for our signer to unblock and provide a commitment point.
-			// During post-funding channel operation, we only advance our point upon
-			// receiving a commitment_signed, and our counterparty cannot send us
-			// another commitment signed until we've provided a new commitment point
-			// in revoke_and_ack, which requires unblocking our signer and completing
-			// the advance to the next point. This should be unreachable since
-			// a new commitment_signed should fail at our signature checks above.
-			debug_assert!(false, "We should be ready to advance our commitment point by the time we receive commitment_signed");
-			return Err(ChannelError::close("Failed to advance our commitment point".to_owned()));
-		}
 		self.context.expecting_peer_commitment_signed = false;
 		// Note that if we need_commitment & !AwaitingRemoteRevoke we'll call
 		// build_commitment_no_status_check() next which will reset this to RAAFirst.