fix bug with headers object and request objects passed into fetch

client/tests/scripts/fetch_once.js

@@ -1,5 +1,13 @@
 async function test() {
+  //regular fetch
   let r = await libcurl.fetch("https://example.com/");
   assert(r.status === 200, "wrong status");
   await r.text();
+
+  //fetch with request object
+  let options = {headers: new Headers({"x-test-header": "1"})};
+  let r2 = await libcurl.fetch(new Request("https://httpbin.org/get", options));
+  assert(r2.status === 200, "wrong status");
+  let r2_json = await r2.json();
+  assert(r2_json.headers["X-Test-Header"] === "1");
 }