test: check endless loop while writing empty string

Refs: #18673
PR-URL: #18924
Refs: #18673
Refs: https://github.com/nodejs/node/blob/v9.5.0/src/node_http2.cc#L1481-L1484
Refs: https://github.com/nodejs/node/blob/v9.5.0/lib/_http_outgoing.js#L659-L661
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

test/parallel/test-http2-client-write-empty-string.js

@@ -0,0 +1,54 @@
+'use strict';
+
+const assert = require('assert');
+const http2 = require('http2');
+
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+
+for (const chunkSequence of [
+  [ '' ],
+  [ '', '' ]
+]) {
+  const server = http2.createServer();
+  server.on('stream', common.mustCall((stream, headers, flags) => {
+    stream.respond({ 'content-type': 'text/html' });
+
+    let data = '';
+    stream.on('data', common.mustNotCall((chunk) => {
+      data += chunk.toString();
+    }));
+    stream.on('end', common.mustCall(() => {
+      stream.end(`"${data}"`);
+    }));
+  }));
+
+  server.listen(0, common.mustCall(() => {
+    const port = server.address().port;
+    const client = http2.connect(`http://localhost:${port}`);
+
+    const req = client.request({
+      ':method': 'POST',
+      ':path': '/'
+    });
+
+    req.on('response', common.mustCall((headers) => {
+      assert.strictEqual(headers[':status'], 200);
+      assert.strictEqual(headers['content-type'], 'text/html');
+    }));
+
+    let data = '';
+    req.setEncoding('utf8');
+    req.on('data', common.mustCallAtLeast((d) => data += d));
+    req.on('end', common.mustCall(() => {
+      assert.strictEqual(data, '""');
+      server.close();
+      client.close();
+    }));
+
+    for (const chunk of chunkSequence)
+      req.write(chunk);
+    req.end();
+  }));
+}