sample_muxer: fix Segment memory leak on error
sample_muxer: fix Segment memory leak on error

use an auto_ptr<mkvparser::Segment> for compatibility which should be
harmless as there is no attempt to transfer ownership; sample.cpp
operates similarly.

Change-Id: I2cb6982aa64c62ff2ec7cbbd646770cb4e782509

webmproject/libwebm,zofuthan/libwebm,webmproject/libwebm,felipebetancur/libwebm,webmproject/libwebm,felipebetancur/libwebm,zofuthan/libwebm