paaudio: try to drain the recording stream

paaudio: try to drain the recording stream

There is no guarantee a single call to pa_stream_peek every
timer_period microseconds can read a recording stream faster
than the data gets produced at the source. Let qpa_read try to
drain the recording stream.

To reproduce the problem:

Start qemu with -audiodev pa,id=audio0,in.mixing-engine=off

On the host connect the qemu recording stream to the monitor of
a hardware output device. While the problem can also be seen
with a hardware input device, it's obvious with the monitor of
a hardware output device.

In the guest start audio recording with audacity and notice the
slow recording data rate.

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Message-id: 20200104091122.13971-4-vr_qemu@t-online.de
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>