### 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
} else if (!t->skeleton) {
					if (t->loc_used) {
						t->loc = t->node_3d->get_position();
					}
					if (t->rot_used) {
						t->rot = t->node_3d->get_quaternion();
					}
					if (t->scale_used) {
						t->scale = t->node_3d->get_scale();
					}
				}
#endif 
			} break;
			case Animation::TYPE_BLEND_SHAPE: {
#ifndef _3D_DISABLED
				TrackCacheBlendShape *t = static_cast<TrackCacheBlendShape *>(track);
				if (t->mesh_3d) {
					t->value = t->mesh_3d->get_blend_shape_value(t->shape_index);
				}
#endif 
			} break;
			case Animation::TYPE_VALUE: {
				TrackCacheValue *t = static_cast<TrackCacheValue *>(track);
				t->value = t->object->get_indexed(t->subpath);
				t->is_continuous = true;
			} break;
			case Animation::TYPE_BEZIER: {
				TrackCacheBezier *t = static_cast<TrackCacheBezier *>(track);
				t->value = t->object->get_indexed(t->subpath);
			} break;