netty: Release SendGrpcFrameCommand when stream is missing (grpc#11116)

`sendGrpcFrame` owns the buffer in `SendGrpcFrameCommand`. If the frame is not handed off to netty, it needs to be released in the method.

grpc#11115

Author: benjaminp

netty/src/main/java/io/grpc/netty/NettyServerHandler.java

@@ -749,6 +749,7 @@ private void sendGrpcFrame(
       int streamId = cmd.stream().id();
       Http2Stream stream = connection().stream(streamId);
       if (stream == null) {
+        cmd.release();
         streamGone(streamId, promise);
         return;
       }