Matroska specs say the number of audio channels defaults to 1 if tag not present.

Change-Id: I868f93c4ed0314d5928ae8222fa2ee6f74e1eeaa
related-to-bug: 3480589
diff --git a/mkvparser/mkvparser.cpp b/mkvparser/mkvparser.cpp
index b4ce5b3..b43b038 100644
--- a/mkvparser/mkvparser.cpp
+++ b/mkvparser/mkvparser.cpp
@@ -3305,7 +3305,7 @@
 AudioTrack::AudioTrack(Segment* pSegment, const Info& i) :

     Track(pSegment, i),

     m_rate(0.0),

-    m_channels(0),

+    m_channels(1),

     m_bitDepth(-1)

 {

     assert(i.type == 2);