### Godot version

4.1.beta (7b1387ff2)

### System information

Mageia 9, Linux

### Issue description

When opening an empty project in latest `master`, I get these errors:
```
ERROR: Index p_idx = -1 is out of bounds (edited_scene.size() = 1).
   at: get_scene_path (editor/scu/../editor_data.cpp:880)
ERROR: Index p_idx = -1 is out of bounds (edited_scene.size() = 1).
   at: check_and_update_scene (editor/scu/../editor_data.cpp:683)
ERROR: Index p_idx = -1 is out of bounds (edited_scene.size() = 1).
   at: set_edited_scene (editor/scu/../editor_data.cpp:745)
```

Possibly related to recent changes to restore past sessions, but there's nothing to restore in this case?

### Steps to reproduce

- Create a new project, edit it
- Quit to project manager
- Re-open the newly created project -> errors

### Minimal reproduction project

Empty project.
if (!docks_visible) {
		for (int i = 0; i < DOCK_SLOT_MAX; i++) {
			dock_slot[i]->hide();
		}
		for (int i = 0; i < vsplits.size(); i++) {
			vsplits[i]->hide();
		}
		right_hsplit->hide();
	} else {
		for (int i = 0; i < DOCK_SLOT_MAX; i++) {
			int tabs_visible = 0;
			for (int j = 0; j < dock_slot[i]->get_tab_count(); j++) {
				if (!dock_slot[i]->is_tab_hidden(j)) {
					tabs_visible++;
				}
			}
			if (tabs_visible) {
				dock_slot[i]->show();
			} else {
				dock_slot[i]->hide();