stream: fix fd is null when calling clearBuffer

PR-URL: https://github.com/nodejs/node/pull/50994
Fixes: https://github.com/nodejs/node/issues/50979
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Raz Luvaton <rluvaton@gmail.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>

lib/internal/streams/writable.js

@@ -733,7 +733,8 @@ function errorBuffer(state) {
 
 // If there's something in the buffer waiting, then process it.
 function clearBuffer(stream, state) {
-  if ((state[kState] & (kDestroyed | kBufferProcessing | kCorked | kBuffered)) !== kBuffered) {
+  if ((state[kState] & (kDestroyed | kBufferProcessing | kCorked | kBuffered | kConstructed)) !==
+      (kBuffered | kConstructed)) {
     return;
   }
 

test/parallel/test-file-write-stream5.js

@@ -0,0 +1,28 @@
+'use strict';
+
+// Test 'uncork' for WritableStream.
+// Refs: https://github.com/nodejs/node/issues/50979
+
+const common = require('../common');
+const fs = require('fs');
+const assert = require('assert');
+const test = require('node:test');
+const tmpdir = require('../common/tmpdir');
+
+const filepath = tmpdir.resolve('write_stream.txt');
+tmpdir.refresh();
+
+const data = 'data';
+
+test('writable stream uncork', () => {
+  const fileWriteStream = fs.createWriteStream(filepath);
+
+  fileWriteStream.on('finish', common.mustCall(() => {
+    const writtenData = fs.readFileSync(filepath, 'utf8');
+    assert.strictEqual(writtenData, data);
+  }));
+  fileWriteStream.cork();
+  fileWriteStream.write(data, common.mustCall());
+  fileWriteStream.uncork();
+  fileWriteStream.end();
+});