http2: delay closing stream

Delay automatically closing the stream with setImmediate in order
to allow any pushStreams to be sent first.
Backport-PR-URL: #22850
PR-URL: #20997Fixes: #20992
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: apapirovski

lib/internal/http2/core.js

@@ -1902,7 +1902,10 @@ class Http2Stream extends Duplex {
 !(state.flags&STREAM_FLAGS_HAS_TRAILERS)&&
 !state.didRead&&
 this._readableState.flowing===null){
-this.close();
+// By using setImmediate we allow pushStreams to make it through
+// before the stream is officially closed. This prevents a bug
+// in most browsers where those pushStreams would be rejected.
+setImmediate(this.close.bind(this));
 }
 }
 }
@@ -2137,7 +2140,7 @@ class ServerHttp2Stream extends Http2Stream {
 letheadRequest=false;
 if(headers[HTTP2_HEADER_METHOD]===HTTP2_METHOD_HEAD)
 headRequest=options.endStream=true;
-options.readable=!options.endStream;
+options.readable=false;
 
 constheadersList=mapToHeaders(headers);
 if(!Array.isArray(headersList))