Let Http2ConnectionHandler close stream with voidPromise (#10819)

Motivation:

Http2ConnectionHandler tries to addListener to the future without checking if it's void. If it is void, this will fail and generate an exception. 
 
Modifications:
Unvoid the promise in writeData()
 
Result:

Fixes #10816, Writing with a voidPromise no longer generates exceptions.

codec-http2/src/main/java/io/netty/handler/codec/http2/DefaultHttp2ConnectionEncoder.java

@@ -120,6 +120,7 @@ public class DefaultHttp2ConnectionEncoder implements Http2ConnectionEncoder, Ht
     @Override
     public ChannelFuture writeData(final ChannelHandlerContext ctx, final int streamId, ByteBuf data, int padding,
             final boolean endOfStream, ChannelPromise promise) {
+        promise = promise.unvoid();
         final Http2Stream stream;
         try {
             stream = requireStream(streamId);

codec-http2/src/test/java/io/netty/handler/codec/http2/Http2ConnectionHandlerTest.java

@@ -656,6 +656,14 @@ public class Http2ConnectionHandlerTest {
         verify(pipeline).fireExceptionCaught(cause);
     }
 
+    @Test
+    public void canCloseStreamWithVoidPromise() throws Exception {
+        handler = newHandler();
+        handler.closeStream(stream, ctx.voidPromise());
+        verify(stream, times(1)).close();
+        verifyNoMoreInteractions(stream);
+    }
+
     @Test
     public void channelReadCompleteTriggersFlush() throws Exception {
         handler = newHandler();