### 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
#ifndef _3D_DISABLED
		bool calc_root = !seeked || is_external_seeking;
#endif 
		for (int i = 0; i < a->get_track_count(); i++) {
			if (!a->track_is_enabled(i)) {
				continue;
			}
			NodePath path = a->track_get_path(i);
			if (!track_cache.has(path)) {
				continue; 
			}
			TrackCache *track = track_cache[path];
			ERR_CONTINUE(!track_map.has(path));
			int blend_idx = track_map[path];
			ERR_CONTINUE(blend_idx < 0 || blend_idx >= track_count);
			real_t blend = blend_idx < track_weights.size() ? track_weights[blend_idx] * weight : weight;
			if (!deterministic) {
				
				
				if (Math::is_zero_approx(track->total_weight)) {
					continue;
				}
				blend = blend / track->total_weight;
			}
			Animation::TrackType ttype = a->track_get_type(i);
			if (ttype != Animation::TYPE_POSITION_3D && ttype != Animation::TYPE_ROTATION_3D && ttype != Animation::TYPE_SCALE_3D && track->type != ttype) {
				
				continue;
			}
			track->root_motion = root_motion_track == path;