Player::Append blocks thread in wasm

[Boneyan]

I try to do simple thing:

1. Call Player::clear() to stop current audio track
2. Immediately after that I call Player::append() to play new track

if !player.empty() {
    player.clear();
}
player.append(sound);

It works fine on linux/windows, but it deadlocks my app thread in WASM.
I have a guess why: inside append there is call to sleep_until_end. sleep_until_end does std::sync::mpsc::Receiver::recv inside of it. And recv blocks calling thread. It causes no issues in linux/windows, because rodio lives in separate thread. But in wasm we have single thread for all things and recv blocks it.
(playing sound on empty Player in WASM works fine)