FilePicker in Flet 0.6.0 pops up 2 windows instead of 1

[ningzichun]

Description

Calling FilePicker on upper view since Flet 0.6.0.dev1309 results in 2 windows popping up instead of the expected 1. This behavior was not present in version 0.5.2.

Code example to reproduce the issue:

import flet as ft

def main(page: ft.Page):
    page.title = "Routes Example"


    file_picker = ft.FilePicker()
    page.overlay.append(file_picker)

    def route_change(route):
        page.views.clear()
        page.views.append(
            ft.View(
                "/",
                [
                    ft.AppBar(title=ft.Text("Flet app"), bgcolor=ft.colors.SURFACE_VARIANT),
                    ft.ElevatedButton("Click this will pop up 1 window",
                        on_click=lambda _: file_picker.pick_files(allow_multiple=True)),
                    ft.ElevatedButton("Visit Store", on_click=lambda _: page.go("/store")),
                ],
            )
        )
        if page.route == "/store":
            page.views.append(
                ft.View(
                    "/store",
                    [
                        ft.AppBar(title=ft.Text("Store"), bgcolor=ft.colors.SURFACE_VARIANT),
                        ft.ElevatedButton("Click this will pop up 2 windows",
                            on_click=lambda _: file_picker.pick_files(allow_multiple=True)),
                        ft.ElevatedButton("Go Home", on_click=lambda _: page.go("/")),
                    ],
                )
            )
        page.update()

    def view_pop(view):
        page.views.pop()
        top_view = page.views[-1]
        page.go(top_view.route)

    page.on_route_change = route_change
    page.on_view_pop = view_pop
    page.go(page.route)


ft.app(target=main)

Describe the results you received:

Describe the results you expected:

The expected behavior is that only 1 window should pop up.

Additional information you deem important (e.g. issue happens only occasionally):

Flet version (pip show flet):

Name: flet
Version: 0.6.0.dev1309
Summary: Flet for Python - easily build interactive multi-platform apps in Python
Home-page: 
Author: Appveyor Systems Inc.
Author-email: hello@flet.dev
License: Apache-2.0
Location: /opt/homebrew/lib/python3.11/site-packages
Requires: flet-core, httpx, oauthlib, packaging, watchdog, websocket-client, websockets
Required-by: 

Operating system:

Tested on MacOS and Windows

Additional environment details:
Python 3.11

[FeodorFitsner]

Will take a look.

Could be related to #1236