http2: simplify subsequent rstStream calls

Do not call destroy each time rstStream is called since the
first call (or receipt of rst frame) will always trigger
destroy. Expand existing test for this behaviour.

PR-URL: #16753
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/internal/http2/core.js

@@ -970,9 +970,8 @@ class Http2Session extends EventEmitter {
 
     const state = stream[kState];
     if (state.rst) {
-      // rst has already been called, do not call again,
-      // skip straight to destroy
-      stream.destroy();
+      // rst has already been called by self or peer,
+      // do not call again
       return;
     }
     state.rst = true;

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

@@ -21,6 +21,10 @@ server.on('listening', common.mustCall(() => {
   // make sure that destroy is called
   req._destroy = common.mustCall(req._destroy.bind(req));
 
+  // second call doesn't do anything
+  assert.doesNotThrow(() => client.rstStream(req, 8));
+  assert.strictEqual(req.rstCode, 0);
+
   req.on('streamClosed', common.mustCall((code) => {
     assert.strictEqual(req.destroyed, true);
     assert.strictEqual(code, 0);