http2: fix reinjection check

We reinject when the sockets has already waiting
data, remarked by @mildsunrise

Co-authored-by: Alba Mendez <me@alba.sh>

PR-URL: #35678
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Alba Mendez <me@alba.sh>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: Ricky Zhou <0x19951125@gmail.com>

lib/internal/http2/core.js

@@ -3110,7 +3110,7 @@ function connect(authority, options, listener) {
   debug('Http2Session connect', options.createConnection);
   // Socket already has some buffered data - emulate receiving it
   // https://github.com/nodejs/node/issues/35475
-  if (typeof options.createConnection === 'function') {
+  if (socket && socket.readableLength) {
     let buf;
     while ((buf = socket.read()) !== null) {
       debug(`Http2Session connect: injecting ${buf.length} already in buffer`);