http2: slightly simplify stream destroy

PR-URL: #16327
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

lib/internal/http2/core.js

@@ -1497,8 +1497,7 @@ class Http2Stream extends Duplex {
     }
 
     const server = session[kServer];
-
-    if (err && server) {
+    if (server !== undefined && err) {
       server.emit('streamError', err, this);
     }
 
@@ -1515,10 +1514,10 @@ function continueStreamDestroy(self, err, callback) {
 
   // Submit RST-STREAM frame if one hasn't been sent already and the
   // stream hasn't closed normally...
-  if (!state.rst && !session.destroyed) {
-    const code =
-      err instanceof Error ?
-        NGHTTP2_INTERNAL_ERROR : NGHTTP2_NO_ERROR;
+  const rst = state.rst;
+  let code = state.rstCode;
+  if (!rst && !session.destroyed) {
+    code = err instanceof Error ? NGHTTP2_INTERNAL_ERROR : NGHTTP2_NO_ERROR;
     session.rstStream(self, code);
   }
 
@@ -1530,13 +1529,10 @@ function continueStreamDestroy(self, err, callback) {
 
   setImmediate(finishStreamDestroy, self, handle);
 
-  // All done
-  const rst = state.rst;
-  const code = rst ? state.rstCode : NGHTTP2_NO_ERROR;
   // RST code 8 not emitted as an error as its used by clients to signify
   // abort and is already covered by aborted event, also allows more
   // seamless compatibility with http1
-  if (!err && code !== NGHTTP2_NO_ERROR && code !== NGHTTP2_CANCEL) {
+  if (code !== NGHTTP2_NO_ERROR && code !== NGHTTP2_CANCEL && !err) {
     err = new errors.Error('ERR_HTTP2_STREAM_ERROR', code);
   }
   callback(err);
@@ -1546,8 +1542,7 @@ function continueStreamDestroy(self, err, callback) {
 
 function finishStreamDestroy(self, handle) {
   const id = self[kID];
-  const session = self[kSession];
-  session[kState].streams.delete(id);
+  self[kSession][kState].streams.delete(id);
   delete self[kSession];
   if (handle !== undefined)
     handle.destroyStream(id);