uninitialized variable in function libavsmash_get_track_by_media_type

[yumetodo]

In function libavsmash_get_track_by_media_type (in libavsmash.c line 109), when track_number is 0 and movie_param.number_of_tracks is 0, track_id will not be initialized.

../common/libavsmash.c: In function 'libavsmash_get_track_by_media_type':
../common/libavsmash.c:175:9: warning: 'track_id' may be used uninitialized in this function [-Wmaybe-uninitialized]
     if( lsmash_construct_timeline( root, track_id ) < 0 )
         ^

GCC warn this.