### 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
}
			
			if (track && (track->type != track_cache_type || ObjectDB::get_instance(track->object_id) == nullptr)) {
				playing_caches.erase(track);
				memdelete(track);
				track_cache.erase(path);
				track = nullptr;
			}
			if (!track) {
				Ref<Resource> resource;
				Vector<StringName> leftover_path;
				Node *child = parent->get_node_and_resource(path, resource, leftover_path);
				if (!child) {
					ERR_PRINT("AnimationMixer: '" + String(E) + "', couldn't resolve track:  '" + String(path) + "'.");
					continue;
				}
				switch (track_type) {
					case Animation::TYPE_VALUE: {
						TrackCacheValue *track_value = memnew(TrackCacheValue);
						if (resource.is_valid()) {
							track_value->object = resource.ptr();
						} else {
							track_value->object = child;
						}
						track_value->is_continuous = anim->value_track_get_update_mode(i) != Animation::UPDATE_DISCRETE;
						track_value->is_using_angle = anim->track_get_interpolation_type(i) == Animation::INTERPOLATION_LINEAR_ANGLE || anim->track_get_interpolation_type(i) == Animation::INTERPOLATION_CUBIC_ANGLE;
						track_value->subpath = leftover_path;
						track_value->object_id = track_value->object->get_instance_id();
						track = track_value;