Error when creating a new project with specific steps (Create Folder manipulation)

### Tested versions

- Reproducible in: v4.3.stable.official [77dcf97d8], v4.4.dev7.official [46c8f8c5c]

### System information

Godot v4.3.stable - Windows 10.0.26100 - Vulkan (Forward+) - dedicated Radeon (TM) RX 480 Graphics - AMD Ryzen 7 2700 Eight-Core Processor (16 Threads)

### Issue description

When trying to create a new project in Godot, if I leave the "Project Name" field empty and uncheck the "Create Folder" option, then check it again and attempt to enter a project name, I encounter the following errors:
- "You cannot save a project at the selected path." (if saving in Documents)
- "The selected path is not empty." (if saving in any other folder)

### Steps to reproduce

1. Open Godot.
2. Click on "Create"
3. Leave the "Project Name" field empty.
4. Uncheck the "Create Folder" option.
5. Check the "Create Folder" option again.
6. Enter a project name.

### Minimal reproduction project (MRP)

N/A

Start by reproducing the project-creation sequence in Godot's Create flow: leave Project Name empty, toggle Create Folder off and on, then enter a name. Trace the validation state after the toggle and confirm that a valid new project path can be created without either path error.

Written by the indexing model from the issue text.