### Godot version

3.5.1mono

### System information

windows10

### Issue description

Error message
 scene/main/node.cpp:1362 - Index p_index = 0 is out of bounds (data.children.size() = 0).
 scene/main/node.cpp:397 - Parameter "p_child" is null.
 scene/gui/tab_container.cpp:593 - Index p_current = 0 is out of bounds (get_tab_count() = 0).
See "Steps to reproduce for details"

### Steps to reproduce

Set an external text editor
Create a script
Drop the script to the built-in text editor like this image:
![image](https://user-images.githubusercontent.com/119792950/209504041-039f2620-5e42-4c0f-8c41-cd24486fb3d2.png)
And got error message:
 scene/main/node.cpp:1362 - Index p_index = 0 is out of bounds (data.children.size() = 0).
 scene/main/node.cpp:397 - Parameter "p_child" is null.
 scene/gui/tab_container.cpp:593 - Index p_current = 0 is out of bounds (get_tab_count() = 0).

### Minimal reproduction project

An empty project
file_dialog->set_file_mode(EditorFileDialog::FILE_MODE_SAVE_FILE);
	file_dialog->set_access(EditorFileDialog::ACCESS_FILESYSTEM);
	file_dialog_option = THEME_SAVE_AS;
	file_dialog->clear_filters();
	file_dialog->add_filter("*.tet");
	file_dialog->set_current_path(EditorPaths::get_singleton()->get_text_editor_themes_dir().path_join(EDITOR_GET("text_editor/theme/color_theme")));
	file_dialog->popup_file_dialog();
	file_dialog->set_title(TTR("Save Theme As..."));
}
bool ScriptEditor::_has_docs_tab() const {
	const int child_count = tab_container->get_tab_count();
	for (int i = 0; i < child_count; i++) {
		if (Object::cast_to<EditorHelp>(tab_container->get_tab_control(i))) {
			return true;
		}
	}
	return false;
}
bool ScriptEditor::_has_script_tab() const {