mkvmuxer: Force new clusters when audio queue gets too long.
mkvmuxer: Force new clusters when audio queue gets too long.

Force creation of a new Cluster when writing queued audio would
cause an error due to violating maximum block duration.

BUG=675521

Change-Id: I6ad09c2a2f71d95bb04eed5ead04dc8072aaa59d

webmproject/libwebm,webmproject/libwebm,webmproject/libwebm