### 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)

return (is_playing() ? playback.assigned : "");
}
void AnimationPlayer::set_assigned_animation(const String &p_anim) {
	if (is_playing()) {
		float speed = get_playing_speed();
		play(p_anim, -1.0, speed, signbit(speed));
	} else {
		ERR_FAIL_COND_MSG(!animation_set.has(p_anim), vformat("Animation not found: %s.", p_anim));
		playback.current.pos = 0;
		playback.current.from = &animation_set[p_anim];
		playback.assigned = p_anim;
	}
}
String AnimationPlayer::get_assigned_animation() const {
	return playback.assigned;
}
void AnimationPlayer::pause() {
	_stop_internal(false, false);
}
void AnimationPlayer::stop(bool p_keep_state) {