### Godot version

v4.2.rc.custom_build [d6a1db2b0]

### System information

Godot v4.2.rc (d6a1db2b0) - Windows 10.0.22621 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3090 Ti (NVIDIA; 31.0.15.4592) - AMD Ryzen 9 7950X 16-Core Processor (32 Threads)

### Issue description

`AnimatedValuesBackup::get_data()` can crash as the internal data map can have nullptr values if any of the tracks were METHOD or ANIMATION types, as `AnimatedValuesBackup::get_cache_copy()` defines that these types of tracks do not get valid copies.

The resulting crash is therefore a null pointer exception.

### Steps to reproduce

1. Open a project with these type of animation tracks.
2. Save the project.

### Minimal reproduction project

https://github.com/godotengine/godot-demo-projects/tree/master/3d/platformer
#ifdef TOOLS_ENABLED
	bool can_call = is_inside_tree() && !Engine::get_singleton()->is_editor_hint();
#endif 
	for (const AnimationInstance &ai : animation_instances) {
		Ref<Animation> a = ai.animation_data.animation;
		double time = ai.playback_info.time;
		double delta = ai.playback_info.delta;
		bool seeked = ai.playback_info.seeked;
		Animation::LoopedFlag looped_flag = ai.playback_info.looped_flag;
		bool is_external_seeking = ai.playback_info.is_external_seeking;
		real_t weight = ai.playback_info.weight;
		Vector<real_t> track_weights = ai.playback_info.track_weights;
		bool backward = signbit(delta);