PTT: Audio capture broken on mobile safari

[dbkr]

Describe the bug
It seems sometimes mobile safari can fail at some point in the audio capture pipeline such that media doesn't get through to the other side and the VU meter rings don't animate on the local capture side.

No media detail available at present.

[robintown]

I presume this was another one of the symptoms fixed by matrix-org/matrix-js-sdk#2484