mkvmuxer: Fix leak when a Cluster isn't finalized

There's a leak in the following scenario:
  * AccurateClusterDuration is set to true.
  * Add a few frames.
  * An error is encountered while adding a frame and the
    application bails without calling Cluster::Finalize
  * All the frames we queues in QueueOrWriteFrames now leak.

This patch fixes this scenario by delete'ing any left over frames
in the Cluster's destructor.

Change-Id: I104f6814db18a86fae9877decfe6cc75b8937fcb
1 file changed