test: http2 rstStream duplicate call

This commit fixes an issue with rstStream() which checked incorrect
value of rst. It also adds a test case for this fix

Refs: #14985

Author: trivikr

lib/internal/http2/core.js

@@ -925,7 +925,7 @@ class Http2Session extends EventEmitter {
                                  'number');
     }
 
-    if (this[kState].rst) {
+    if (stream[kState].rst) {
       // rst has already been called, do not call again,
       // skip straight to destroy
       stream.destroy();

test/parallel/test-http2-client-rststream-before-connect.js

@@ -15,12 +15,15 @@ server.on('listening', common.mustCall(() => {
   const client = h2.connect(`http://localhost:${server.address().port}`);
 
   const req = client.request({ ':path': '/' });
+  // make sure that destroy is called twice
+  req._destroy = common.mustCall(req._destroy.bind(req), 2);
+
   client.rstStream(req, 0);
+  // redundant call to rstStream with new code
+  client.rstStream(req, 1);
+  // confirm that rstCode is from the first call to rstStream
   assert.strictEqual(req.rstCode, 0);
 
-  // make sure that destroy is called
-  req._destroy = common.mustCall(req._destroy.bind(req));
-
   req.on('streamClosed', common.mustCall((code) => {
     assert.strictEqual(req.destroyed, true);
     assert.strictEqual(code, 0);