url: fix URL query update if searchParams changes

If searchParams becomes empty, query must be set to null.
Add missing update of context flags.

Fixes: #10480
PR-URL: #10486
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/internal/url.js

@@ -593,7 +593,15 @@ function update(url, params) {
  if (!url)
    return;

  url[context].query = params.toString();
  const ctx = url[context];
  const serializedParams = params.toString();
  if (serializedParams) {
    ctx.query = serializedParams;
    ctx.flags |= binding.URL_FLAGS_HAS_QUERY;
  } else {
    ctx.query = null;
    ctx.flags &= ~binding.URL_FLAGS_HAS_QUERY;
  }
}

function getSearchParamPairs(target) {

test/parallel/test-whatwg-url-searchparams-delete.js

@@ -42,3 +42,15 @@ params.append('first', 10);
params.delete('first');
assert.strictEqual(false, params.has('first'),
                   'Search params object has no "first" name');

// https://github.com/nodejs/node/issues/10480
// Emptying searchParams should correctly update url's query
{
  const url = new URL('http://domain?var=1&var=2&var=3');
  for (const param of url.searchParams.keys()) {
    url.searchParams.delete(param);
  }
  assert.strictEqual(url.searchParams.toString(), '');
  assert.strictEqual(url.search, '');
  assert.strictEqual(url.href, 'http://domain/');
}