Avoid panics returning error instead (#509)

# Description

Improve robustness by replacing `.expect()` calls with proper error
handling in `opening.rs`.

Instead of panicking when `on_noise_channel_open()` or
`on_noise_channel_data()` fail, the errors are now logged and the
connection is gracefully closed by returning
`WebRtcEvent::ConnectionClosed`

Closes #350
Closes ChainSafe/gossamer-parity#77

Author: dimartiro

src/transport/webrtc/opening.rs

@@ -409,8 +409,15 @@ impl OpeningWebRtcConnection {
                             continue;
                         }
 
-                        // TODO: https://github.com/paritytech/litep2p/issues/350 no expect
-                        self.on_noise_channel_open().expect("to succeed");
+                        if let Err(error) = self.on_noise_channel_open() {
+                            tracing::debug!(
+                                target: LOG_TARGET,
+                                connection_id = ?self.connection_id,
+                                ?error,
+                                "noise channel open failed",
+                            );
+                            return WebRtcEvent::ConnectionClosed;
+                        }
                     }
                     Event::ChannelData(data) => {
                         tracing::trace!(
@@ -428,8 +435,18 @@ impl OpeningWebRtcConnection {
                             continue;
                         }
 
-                        // TODO: https://github.com/paritytech/litep2p/issues/350 no expect
-                        return self.on_noise_channel_data(data.data).expect("to succeed");
+                        match self.on_noise_channel_data(data.data) {
+                            Ok(event) => return event,
+                            Err(error) => {
+                                tracing::debug!(
+                                    target: LOG_TARGET,
+                                    connection_id = ?self.connection_id,
+                                    ?error,
+                                    "noise channel data handling failed",
+                                );
+                                return WebRtcEvent::ConnectionClosed;
+                            }
+                        }
                     }
                     Event::ChannelClose(channel_id) => {
                         tracing::debug!(target: LOG_TARGET, ?channel_id, "channel closed");