### 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)

if (len > pasi.len) {
					stop = true;
				}
			}
			if (stop) {
				
				aa->audio_stream_playback->stop_stream(pasi.index);
				erase_list.push_back(K.key);
			}
		}
		for (uint32_t erase_idx = 0; erase_idx < erase_list.size(); erase_idx++) {
			aa->playing_streams.erase(erase_list[erase_idx]);
		}
	}
}
void AnimationPlayer::_animation_process(double p_delta) {
	if (playback.current.from) {
		end_reached = false;
		end_notify = false;
		bool started = playback.started; 
		if (playback.started) {
			playback.started = false;
		}
		cache_update_size = 0;
		cache_update_prop_size = 0;
		cache_update_bezier_size = 0;
		cache_update_audio_size = 0;
		AnimationData *prev_from = playback.current.from;
		_animation_process2(p_delta, started);
		if (prev_from != playback.current.from) {