src: combine loops in CopyJsStringArray()

In spawn_sync.cc, two consecutive loops are used to convert
data to strings, and compute the size of the data. This commit
merges the two independent loops into one.

Refs: nodejs/node#15380
PR-URL: nodejs/node#16247
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/spawn_sync.cc

@@ -1016,25 +1016,22 @@ int SyncProcessRunner::CopyJsStringArray(Local<Value> js_value,
  Local<Context> context = env()->context();
  js_array = js_value.As<Array>()->Clone().As<Array>();
  length = js_array->Length();
+ data_size = 0;
+
+ // Index has a pointer to every string element, plus one more for a final
+ // null pointer.
+ list_size = (length + 1) * sizeof *list;
 
  // Convert all array elements to string. Modify the js object itself if
- // needed - it's okay since we cloned the original object.
+ // needed - it's okay since we cloned the original object. Also compute the
+ // length of all strings, including room for a null terminator after every
+ // string. Align strings to cache lines.
  for (uint32_t i = 0; i < length; i++) {
  auto value = js_array->Get(context, i).ToLocalChecked();
 
  if (!value->IsString())
  js_array->Set(context, i, value->ToString(env()->isolate())).FromJust();
- }
 
- // Index has a pointer to every string element, plus one more for a final
- // null pointer.
- list_size = (length + 1) * sizeof *list;
-
- // Compute the length of all strings. Include room for null terminator
- // after every string. Align strings to cache lines.
- data_size = 0;
- for (uint32_t i = 0; i < length; i++) {
- auto value = js_array->Get(context, i).ToLocalChecked();
  data_size += StringBytes::StorageSize(isolate, value, UTF8) + 1;
  data_size = ROUND_UP(data_size, sizeof(void*));
  }