Opening DatePicker returns AssertionError
### Duplicate Check

- [X] I have searched the [opened issues](https://github.com/flet-dev/flet/issues) and there are no duplicates

### Describe the bug

When running example from docs, clicking on Pick Date button, which opens DatePicker, returns an error:

Future exception was never retrieved
future: <Future finished exception=AssertionError('last_date must be on or after current_date')>
Traceback (most recent call last):
  File "/Users/inesa/.pyenv/versions/3.12.6/lib/python3.12/concurrent/futures/thread.py", line 58, in run
    result = self.fn(*self.args, **self.kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/inesa/projects/flet-dev/flet/sdk/python/packages/flet/src/flet/core/page.py", line 948, in wrapper
    handler(*args)
  File "/Users/inesa/projects/flet-dev/flet/sdk/python/playground/date-picker-test.py", line 19, in <lambda>
    on_click=lambda e: page.open(
                       ^^^^^^^^^^
  File "/Users/inesa/projects/flet-dev/flet/sdk/python/packages/flet/src/flet/core/page.py", line 1429, in open
    self.__offstage.update()
  File "/Users/inesa/projects/flet-dev/flet/sdk/python/packages/flet/src/flet/core/control.py", line 324, in update
    self.__page.update(self)
  File "/Users/inesa/projects/flet-dev/flet/sdk/python/packages/flet/src/flet/core/page.py", line 723, in update
    r = self.__update(*controls)
        ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/inesa/projects/flet-dev/flet/sdk/python/packages/flet/src/flet/core/page.py", line 835, in __update
    commands, added_controls, removed_controls = self.__prepare_update(*controls)
                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/inesa/projects/flet-dev/flet/sdk/python/packages/flet/src/flet/core/page.py", line 851, in __prepare_update
    control.build_update_commands(
  File "/Users/inesa/projects/flet-dev/flet/sdk/python/packages/flet/src/flet/core/control.py", line 498, in build_update_commands
    innerCmds = ctrl._build_add_commands(
                ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/inesa/projects/flet-dev/flet/sdk/python/packages/flet/src/flet/core/control.py", line 552, in _build_add_commands
    command = self._build_command(False)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/inesa/projects/flet-dev/flet/sdk/python/packages/flet/src/flet/core/control.py", line 579, in _build_command
    self.before_update()
  File "/Users/inesa/projects/flet-dev/flet/sdk/python/packages/flet/src/flet/core/date_picker.py", line 189, in before_update
    self.__last_date is None

### Code sample

<details open><summary>Code</summary>

```python
import datetime
import flet as ft


def main(page: ft.Page):
    page.horizontal_alignment = ft.CrossAxisAlignment.CENTER

    def handle_change(e):
        page.add(ft.Text(f"Date changed: {e.control.value.strftime('%Y-%m-%d')}"))

    def handle_dismissal(e):
        page.add(ft.Text(f"DatePicker dismissed"))

    page.add(
        ft.ElevatedButton(
            "Pick date",
            icon=ft.icons.CALENDAR_MONTH,
            on_click=lambda e: page.open(
                ft.DatePicker(
                    first_date=datetime.datetime(year=2023, month=10, day=1),
                    last_date=datetime.datetime(year=2024, month=10, day=1),
                    on_change=handle_change,
                    on_dismiss=handle_dismissal,
                )
            ),
        )
    )


ft.app(main)
```

</details>


### To reproduce

1. Run Code sample
2. Click on "Pick date" button -> see the error in output

### Expected behavior

expected to see the DatePicker

### Screenshots / Videos

<details open>
<summary>Captures</summary>

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</details>


### Operating System

macOS

### Operating system details

macOs

### Flet version

flet==0.25.0.dev3750

### Regression

Yes, it used to work in a previous Flet version (please specify the version in additional details)

### Suggestions

_No response_

### Logs

<details open><summary>Logs</summary>

```console
[Paste your logs here]
```

</details>


### Additional details

_No response_