Comment 24 for bug 1556439

I checked all pa_sink_input_unlink() and pa_sink_input_kill() calls, and I didn't notice anything that could cause a sink input to be unlinked while it's being moved, so it looks like this crash should be impossible... Oh well, there's a fix and the fix seems sensible in any case, so I'm not going to spend more time on this (unless it's reported that the fix doesn't help).