First IME-composed character is lost when typing into an empty block with fontSizeDefaultSelection set (Windows)

When `fontSizeDefaultSelection` is configured (to any value other than the default `"Font Size"`) together with the `font_size` plugin, typing the first character of a Japanese IME composition into an empty block (e.g. a newly created empty paragraph) causes that character to be silently dropped on Windows.

## To Reproduce

Steps to reproduce the behavior:

1. Open the editor with some existing text wrapped in a paragraph, e.g. `<p>abc</p>` (plain unwrapped text does not reproduce the issue)
2. Place the cursor at the end of the text and press Enter to create a new empty paragraph
3. With the IME in Japanese (romaji) input mode, type `AIUEO`

JSFiddle reproduction: https://jsfiddle.net/zj1kwt74/

```html
<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <script src="https://cdn.jsdelivr.net/npm/froala-editor@5.2.0/js/froala_editor.min.js"></script>
  <script src="https://cdn.jsdelivr.net/npm/froala-editor@5.2.0/js/plugins/font_size.min.js"></script>
  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/froala-editor@5.2.0/css/froala_style.min.css">
  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/froala-editor@5.2.0/css/froala_editor.pkgd.min.css">
</head>
<body>
  <textarea id="froala-editor">&lt;p&gt;abc&lt;/p&gt;</textarea>
  <script>
    new FroalaEditor('#froala-editor', {
      key: '',
      fontSizeDefaultSelection: '20'
    });
  </script>
</body>
</html>
```

### Expected behavior
Typing `AIUEO` via the Japanese IME should produce `あいうえお` (as it does when `fontSizeDefaultSelection` is not set).

### Actual behavior
The first character (`A`) is dropped entirely. The IME only confirms `いうえお`, missing the initial `あ`. The resulting HTML shows the default font size having been applied to the content, e.g.:
```html
<p><span style="font-size: 20px;">いうえお</span></p>
```

https://github.com/user-attachments/assets/dc228a95-fff7-4c10-b824-9326b760863f

## Environment

- **Froala Editor version:** 5.2.0
- **OS:** Windows 11 (Windows 11 Pro / 25H2 / 26200.8653)
- **Browser:** Edge (149.0.4022.98)
- **IME:** Microsoft IME romaji-to-kana input mode

## Additional context

This does not reproduce on macOS (Chrome) under the same steps — it appears to be Windows-specific.

As a workaround, not setting `fontSizeDefaultSelection` avoids the issue entirely.

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First IME-composed character is lost when typing into an empty block with fontSizeDefaultSelection set (Windows) #5057

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First IME-composed character is lost when typing into an empty block with fontSizeDefaultSelection set (Windows) #5057

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