src,crypto: fix 0-length output crash in webcrypto

Refs: nodejs#38883

src/crypto/crypto_cipher.h

@@ -249,7 +249,7 @@ class CipherJob final : public CryptoJob<CipherTraits> {
       v8::Local<v8::Value>* result) override {
     Environment* env = AsyncWrap::env();
     CryptoErrorStore* errors = CryptoJob<CipherTraits>::errors();
-    if (out_.size() > 0) {
+    if (out_.size() > 0 || (!out_.size() && errors->Empty())) {
       CHECK(errors->Empty());
       *err = v8::Undefined(env->isolate());
       *result = out_.ToArrayBuffer(env);

test/parallel/test-crypto-subtle-zero-length.js

@@ -0,0 +1,38 @@
+'use strict';
+
+const common = require('../common');
+
+const assert = require('assert');
+const crypto = require('crypto').webcrypto;
+
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+
+crypto.subtle.importKey(
+  'raw',
+  new Uint8Array(32),
+  { name: 'AES-GCM' },
+  false,
+  [ 'encrypt','decrypt' ]).then(k => {
+    assert(k instanceof crypto.CryptoKey);
+    return crypto.subtle.encrypt({
+      name: 'AES-GCM',
+      iv: new Uint8Array(12),
+    }, k, new Uint8Array(0)).then(e => {
+      assert(e instanceof ArrayBuffer);
+      assert.deepStrictEqual(
+        Buffer.from(e),
+        Buffer.from([
+          0x53, 0x0f, 0x8a, 0xfb, 0xc7, 0x45, 0x36, 0xb9,
+          0xa9, 0x63, 0xb4, 0xf1, 0xc4, 0xcb, 0x73, 0x8b ]));
+      return crypto.subtle.decrypt({
+        name: 'AES-GCM',
+        iv: new Uint8Array(12) },
+        k,
+        e);
+    });
+  })
+  .then(v => {
+    assert(v instanceof ArrayBuffer);
+    assert.strictEqual(v.byteLength, 0);
+  });