`m_deviceInfo->hostApi` is an index in the list of supported APIs on
this platform. So on Linux 0 is ALSA, 2 is JACK. This is also mentioned
in the comment on the `hostApi` field. We should be checking the device
type ID instead, as is done elsewhere in the code.

This fixes the buffer size when using JACK clients. With JACK the buffer
size should be coming from the server (and PortAudio chops it up into
1024 sample blocks if it's larger). Before this change it would use the
now grayed out latency value set for the previous audio backend before
switching to JACK (defaulting to 1024 samples).

In any operation that works with audio buffers passed from PortAudio.
This is needed because PortAudio may pass us buffers that are smaller or
larger than the size we request. And when using JACK the requested size
is 0, which will cause PortAudio to pick a buffer size matching the JACK
server.

The network backend already does this.

to clarify that thisis not the actually used value. The actual value is
passied via every audi callback.

…ments.

This clarifies that the value is a subject of change in case of JACK

This allows following the server buffer size that is not always const.