Add missing return which could lead to double notification of a promise and so unexpected exception (#845)

Motivation:

When we fail the promise because of an unsupported message we need to
return early.

Modifications:

Add missing return

Result:

Correctly handle unsupported messages

Author: normanmaurer

codec-classes-quic/src/main/java/io/netty/incubator/codec/quic/QuicheQuicStreamChannel.java

@@ -795,6 +795,7 @@ void writeWithoutCheckChannelState(Object msg, ChannelPromise promise) {
             } catch (UnsupportedOperationException e) {
                 ReferenceCountUtil.release(msg);
                 promise.setFailure(e);
+                return;
             }
 
             boolean wasFinSent = QuicheQuicStreamChannel.this.finSent;