### 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
prev_time = Math::fposmod(prev_time, (double)a->get_length());
									} break;
									case Animation::LOOP_PINGPONG: {
										prev_time = Math::pingpong(prev_time, (double)a->get_length());
									} break;
									default:
										break;
								}
							}
						}
						Quaternion rot[2];
						if (!backward) {
							if (prev_time > time) {
								Error err = a->try_rotation_track_interpolate(i, prev_time, &rot[0]);
								if (err != OK) {
									continue;
								}
								rot[0] = post_process_key_value(a, i, rot[0], t->object, t->bone_idx);
								a->try_rotation_track_interpolate(i, (double)a->get_length(), &rot[1]);
								rot[1] = post_process_key_value(a, i, rot[1], t->object, t->bone_idx);
								root_motion_cache.rot = (root_motion_cache.rot * Quaternion().slerp(rot[0].inverse() * rot[1], blend)).normalized();
								prev_time = 0;
							}
						} else {
							if (prev_time < time) {
								Error err = a->try_rotation_track_interpolate(i, prev_time, &rot[0]);
								if (err != OK) {
									continue;
								}
								rot[0] = post_process_key_value(a, i, rot[0], t->object, t->bone_idx);