http2: no crash on stream listener removal w/ destroyed session

Do not crash when the session is no longer available.

Fixes: nodejs#29457

lib/internal/http2/core.js

@@ -426,23 +426,27 @@ function sessionListenerRemoved(name) {
 // Also keep track of listeners for the Http2Stream instances, as some events
 // are emitted on those objects.
 function streamListenerAdded(name) {
+  const session = this[kSession];
+  if (!session) return;
   switch (name) {
     case 'priority':
-      this[kSession][kNativeFields][kSessionPriorityListenerCount]++;
+      session[kNativeFields][kSessionPriorityListenerCount]++;
       break;
     case 'frameError':
-      this[kSession][kNativeFields][kSessionFrameErrorListenerCount]++;
+      session[kNativeFields][kSessionFrameErrorListenerCount]++;
       break;
   }
 }
 
 function streamListenerRemoved(name) {
+  const session = this[kSession];
+  if (!session) return;
   switch (name) {
     case 'priority':
-      this[kSession][kNativeFields][kSessionPriorityListenerCount]--;
+      session[kNativeFields][kSessionPriorityListenerCount]--;
       break;
     case 'frameError':
-      this[kSession][kNativeFields][kSessionFrameErrorListenerCount]--;
+      session[kNativeFields][kSessionFrameErrorListenerCount]--;
       break;
   }
 }

test/parallel/test-http2-stream-removelisteners-after-close.js

@@ -0,0 +1,31 @@
+'use strict';
+
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+const http2 = require('http2');
+
+// Regression test for https://github.com/nodejs/node/issues/29457:
+// HTTP/2 stream event listeners can be added and removed after the
+// session has been destroyed.
+
+const server = http2.createServer((req, res) => {
+  res.end('Hi!\n');
+});
+
+server.listen(0, common.mustCall(() => {
+  const client = http2.connect(`http://localhost:${server.address().port}`);
+  const headers = { ':path': '/' };
+  const req = client.request(headers);
+
+  req.on('close', common.mustCall(() => {
+    req.removeAllListeners();
+    req.on('priority', common.mustNotCall());
+    server.close();
+  }));
+
+  req.on('priority', common.mustNotCall());
+  req.on('error', common.mustCall());
+
+  client.destroy();
+}));