### Godot version

4.0.beta13

### System information

Windows 10

### Issue description

When you call the `seek()` function without a current animation it outputs `Condition "!playback.current.from" is true.` to the debugger.

I was getting the error above whenever I would call `stop()` on an AnimationPlayer when it didn't have a playing animation. I realized that `stop()` also calls the `seek()` function.

I would expect the `seek()` and `stop()` functions to just do nothing, instead of throwing errors, if there isn't a current animation, or at least show an error that says that there is no animation to seek/stop.

This is the same issue that was described here: [#6122](https://github.com/godotengine/godot/issues/6122)

### Steps to reproduce

- Create an AnimationPlayer node.
- Don't have it play any animations.
- Call the `seek()` function.

### Minimal reproduction project

[seek_issue.zip](https://github.com/godotengine/godot/files/10442071/seek_issue.zip)

Ref<AnimatedValuesBackup> backup;
	if (!playback.current.from) {
		return backup;
	}
	_ensure_node_caches(playback.current.from, p_root_override);
	backup.instantiate();
	for (int i = 0; i < playback.current.from->node_cache.size(); i++) {
		TrackNodeCache *nc = playback.current.from->node_cache[i];
		if (!nc) {
			continue;
		}
		if (nc->skeleton) {
			if (nc->bone_idx == -1) {
				continue;
			}
			AnimatedValuesBackup::Entry entry;
			entry.object = nc->skeleton;
			entry.bone_idx = nc->bone_idx;
			Array arr;
			arr.resize(3);
			arr[0] = nc->skeleton->get_bone_pose_position(nc->bone_idx);