avformat/dashdec: Fix leak of representation on error
If parsing a representation fails, it is not added to the list of
representations and is therefore not freed in dash_close(); it therefore
leaked in most error paths in parse_manifest_representation() (some
error paths had (incomplete) code for freeing). This commit fixes
freeing the representation in this case.
Reviewed-by: Steven Liu <lq@chinaffmpeg.org> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>