Stopping recording before encoder loaded results in failure

[entr0cks]

Using .stopRecording() results in a bad file when encoder (mp3) hasn't loaded yet, since it relies on a worker that hasn't loaded yet.
Also, although the resulting file can't be played, its size indicates that it's not processed.

To reproduce you can use this demo (https://addpipe.com/simple-web-audio-recorder-demo/) and throttle networking with Devtools for Chrome (for example 800kb/s) and do a short 1-2s recording.

The log of the demo should display:
Loading mp3 encoder...
Recording started
Recording stopped
mp3 encoder loaded
Encoding complete