Update ixBidAdapter.js (#5289)

* Update ixBidAdapter.js

If the Index adapter is aliased, this gathers the alias instead of using the hard coded 'ix' value for bidder code.

* check for existence of bidderrequest

bidderrequest object doesn't exist in the test spec; IX team may want to write a more extensive test here.

modules/ixBidAdapter.js

@@ -287,7 +287,8 @@ function buildRequest(validBidRequests, bidderRequest, impressions, version) {
   const payload = {};
 
   // Parse additional runtime configs.
-  const otherIxConfig = config.getConfig('ix');
+  const bidderCode = (bidderRequest && bidderRequest.bidderCode) || 'ix';
+  const otherIxConfig = config.getConfig(bidderCode);
   if (otherIxConfig) {
     // Append firstPartyData to r.site.page if firstPartyData exists.
     if (typeof otherIxConfig.firstPartyData === 'object') {