onLoadMore is called when ComboBox tray is opened

# 🐛 Bug Report

Related to https://github.com/adobe/react-spectrum/issues/2365, caught during subsequent testing. Looks like the fix provided doesn't quite work for the ComboBox tray case, onLoadMore is still called every time the tray opens regardless of the number of items that are already loaded.

## 🤔 Expected Behavior

onLoadMore shouldn't be called when the combobox tray opens and there are enough items loaded to populate the tray height * 1.5

## 😯 Current Behavior

onLoadMore is always called on ComboBox tray open.

## 🌍 Your Environment

| Software | Version(s) |
| ---------------- | ---------- |
| react-spectrum |. 3.15
| Browser |
| Operating System |

## 🧢 Your Company/Team

RSP