http: lazy allocate cookies array

lib/_http_outgoing.js

@@ -673,20 +673,22 @@ OutgoingMessage.prototype.setHeaders = function setHeaders(headers) {
   // We also cannot safely split by comma.
   // To avoid setHeader overwriting the previous value we push
   // set-cookie values in array and set them all at once.
-  const cookies = [];
+  let cookies = null;
 
   for (const { 0: key, 1: value } of headers) {
     if (key === 'set-cookie') {
       if (ArrayIsArray(value)) {
+        cookies ??= [];
         cookies.push(...value);
       } else {
+        cookies ??= [];
         cookies.push(value);
       }
       continue;
     }
     this.setHeader(key, value);
   }
-  if (cookies.length) {
+  if (cookies != null) {
     this.setHeader('set-cookie', cookies);
   }