Don't fade out after pausing unless stream is running

(cherry picked from commit eb5566f5c5f6ed6171a9d271ffff766e7a9f8a04)

scene/audio/audio_stream_player.cpp

@@ -107,7 +107,7 @@ void AudioStreamPlayer::_mix_audio() {
 	}
 
 	if (stream_paused) {
-		if (stream_paused_fade) {
+		if (stream_paused_fade && stream_playback->is_playing()) {
 			_mix_internal(true);
 			stream_paused_fade = false;
 		}