Jacek Tomaszewski authored Dec 12, 2018 and Nirbheek Chauhan committed Jan 21, 2019

'channel-mask' field should not be put in caps if channel mask is 0x0

Mapping WASAPI channel mask to GST equivalent was going only over
first nChannels elements of wasapi_to_gst_pos array, translating, for
example, WASAPI's 0x63f to GST's 0x3f instead of 0xc3f.

When 'channel-mask' is specified as NULL, it signifies that there's
need to do downmix or upmix and it makes caps negotiation with
audioconvert element impossible. Just omit it.

Signed-off-by: Nirbheek Chauhan <nirbheek@centricular.com>