### 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
root_motion_scale = root_motion_cache.scale - Vector3(1, 1, 1);
					root_motion_position_accumulator = t->loc;
					root_motion_rotation_accumulator = t->rot;
					root_motion_scale_accumulator = t->scale;
				} else if (t->skeleton && t->bone_idx >= 0) {
					if (t->loc_used) {
						t->skeleton->set_bone_pose_position(t->bone_idx, t->loc);
					}
					if (t->rot_used) {
						t->skeleton->set_bone_pose_rotation(t->bone_idx, t->rot);
					}
					if (t->scale_used) {
						t->skeleton->set_bone_pose_scale(t->bone_idx, t->scale);
					}
				} else if (!t->skeleton) {
					if (t->loc_used) {
						t->node_3d->set_position(t->loc);
					}
					if (t->rot_used) {
						t->node_3d->set_rotation(t->rot.get_euler());
					}
					if (t->scale_used) {
						t->node_3d->set_scale(t->scale);
					}
				}
#endif 
			} break;
			case Animation::TYPE_BLEND_SHAPE: {
#ifndef _3D_DISABLED
				TrackCacheBlendShape *t = static_cast<TrackCacheBlendShape *>(track);