osxaudio: fix latency property query on RemoteIO
osxaudio: fix latency property query on RemoteIO

AudioUnitGetProperty would fail with kParamErr (-50) every time,
simply because size wasn't initialized.

Now it returns zero latency, but at least it doesn't fail.

https://bugzilla.gnome.org/show_bug.cgi?id=750868

hizukiayaka/gst-plugins-good,Kurento/gst-plugins-good,rawoul/gst-plugins-good,rawoul/gst-plugins-good,GStreamer/gst-plugins-good,kittee/gst-plugins-good,GStreamer/gst-plugins-good,hizukiayaka/gst-plugins-good,hizukiayaka/gst-plugins-good,rawoul/gst-plugins-good,froggatt/gst-plugins-good-m,GrokImageCompression/gst-plugins-good,StreamUtils/gst-plugins-good,sebras/gst-plugins-good,shelsonjava/gst-plugins-good,stfl/gst-plugins-good,GrokImageCompression/gst-plugins-good,shelsonjava/gst-plugins-good,sebras/gst-plugins-good,vatavuserban/gst-plugins-good,chamois94/gst-plugins-good,rawoul/gst-plugins-good,chamois94/gst-plugins-good,StreamUtils/gst-plugins-good,kittee/gst-plugins-good,Kurento/gst-plugins-good,GrokImageCompression/gst-plugins-good,GrokImageCompression/gst-plugins-good,stfl/gst-plugins-good,GStreamer/gst-plugins-good,stfl/gst-plugins-good,vatavuserban/gst-plugins-good,stfl/gst-plugins-good,sebras/gst-plugins-good,shelsonjava/gst-plugins-good,vatavuserban/gst-plugins-good,ikonst/gst-plugins-good,pexip/gst-plugins-good,chamois94/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,kittee/gst-plugins-good,shelsonjava/gst-plugins-good,kittee/gst-plugins-good,vatavuserban/gst-plugins-good,ikonst/gst-plugins-good,froggatt/gst-plugins-good-m,pexip/gst-plugins-good,ikonst/gst-plugins-good,froggatt/gst-plugins-good-m,StreamUtils/gst-plugins-good,chamois94/gst-plugins-good,Kurento/gst-plugins-good,Kurento/gst-plugins-good,froggatt/gst-plugins-good-m,Kurento/gst-plugins-good,StreamUtils/gst-plugins-good,sebras/gst-plugins-good,pexip/gst-plugins-good,ikonst/gst-plugins-good,hizukiayaka/gst-plugins-good,pexip/gst-plugins-good