### 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::pingpong(prev_time, (double)a->get_length());
									} break;
									default:
										break;
								}
							}
						}
						Vector3 scale[2];
						if (!backward) {
							if (prev_time > time) {
								Error err = a->try_scale_track_interpolate(i, prev_time, &scale[0]);
								if (err != OK) {
									continue;
								}
								scale[0] = post_process_key_value(a, i, scale[0], t->object, t->bone_idx);
								a->try_scale_track_interpolate(i, (double)a->get_length(), &scale[1]);
								root_motion_cache.scale += (scale[1] - scale[0]) * blend;
								scale[1] = post_process_key_value(a, i, scale[1], t->object, t->bone_idx);
								prev_time = 0;
							}
						} else {
							if (prev_time < time) {
								Error err = a->try_scale_track_interpolate(i, prev_time, &scale[0]);
								if (err != OK) {
									continue;
								}
								scale[0] = post_process_key_value(a, i, scale[0], t->object, t->bone_idx);
								a->try_scale_track_interpolate(i, 0, &scale[1]);
								scale[1] = post_process_key_value(a, i, scale[1], t->object, t->bone_idx);
								root_motion_cache.scale += (scale[1] - scale[0]) * blend;