### 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
}
								loc[0] = post_process_key_value(a, i, loc[0], t->object, t->bone_idx);
								a->try_position_track_interpolate(i, 0, &loc[1]);
								loc[1] = post_process_key_value(a, i, loc[1], t->object, t->bone_idx);
								root_motion_cache.loc += (loc[1] - loc[0]) * blend;
								prev_time = (double)a->get_length();
							}
						}
						Error err = a->try_position_track_interpolate(i, prev_time, &loc[0]);
						if (err != OK) {
							continue;
						}
						loc[0] = post_process_key_value(a, i, loc[0], t->object, t->bone_idx);
						a->try_position_track_interpolate(i, time, &loc[1]);
						loc[1] = post_process_key_value(a, i, loc[1], t->object, t->bone_idx);
						root_motion_cache.loc += (loc[1] - loc[0]) * blend;
						prev_time = !backward ? 0 : (double)a->get_length();
					}
					{
						Vector3 loc;
						Error err = a->try_position_track_interpolate(i, time, &loc);
						if (err != OK) {
							continue;
						}
						loc = post_process_key_value(a, i, loc, t->object, t->bone_idx);
						t->loc += (loc - t->init_loc) * blend;
					}
#endif 
				} break;
				case Animation::TYPE_ROTATION_3D: {