Nodes 2.0: setting an empty value in combo boxes when pressing Enter in incomplete search

### Prerequisites

- [x] I am running the latest version of ComfyUI
- [x] I have searched existing issues to make sure this isn't a duplicate
- [x] I have tested with all custom nodes disabled ([see how](https://docs.comfy.org/troubleshooting/custom-node-issues#step-1%3A-test-with-all-custom-nodes-disabled))

### What happened?

Easier to explain with a video, comparing the behaviour with the previous Nodes version:

https://github.com/user-attachments/assets/428b9f73-1f76-4a4e-9fe5-c6dbf633f8ca

This is actually two usability issues in one:

- The search field is not focused by default, so unless the user waste an extra click on it, it's very easy to accidentally press a shortcut - like what happens in the video, where I start the search entering R, and the UI refreshes node definitions instead of starting the search.
- After entering the first letters of my value, I press Enter with the intention to select the first match. However, that sets an empty value instead.

### Steps to Reproduce

1. Click on a combo box to bring up the search field.
2. If you start typing away, it won't start the search. You must press the search field fist.
3. Type the first few characters of your option
4. Press Enter without completing your search. The combo box will be updated with an empty value instead of the best match, as it used to do in the previous Nodes.

The workflow runs, but you can't tell which value is selected.

### How is this affecting you?

Visual/UI issue only

### ComfyUI Frontend Version

1.34.2

### Browser

Chrome/Chromium

### Console Errors

```javascript

```

### Logs

```shell

```

### Additional Context

_No response_

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-7038-Nodes-2-0-setting-an-empty-value-in-combo-boxes-when-pressing-Enter-in-incomplete-sea-2ba6d73d36508163a318fc3bd30038de) by [Unito](https://www.unito.io)