Ensure valid host when opening native window (#4443)

This PR fixes #4438, which describes that using `ui.run(host='0.0.0.0',
native=True)` is currently broken. The problem is that `0.0.0.0` is an
placeholder to tell the operating system to bind to all interfaces. But
`0.0.0.0` is not a valid IP to be accessed. So we need to make sure to
not pass it to the native browser window.

nicegui/ui_run.py

@@ -176,7 +176,8 @@ def run(*,
         host = host or '127.0.0.1'
         port = port or native_module.find_open_port()
         width, height = window_size or (800, 600)
-        native_module.activate(host, port, title, width, height, fullscreen, frameless)
+        native_host = '127.0.0.1' if host == '0.0.0.0' else host
+        native_module.activate(native_host, port, title, width, height, fullscreen, frameless)
     else:
         port = port or 8080
         host = host or '0.0.0.0'