avformat/matroskadec: Simplify control flow of parsing laces

avformat/matroskadec: Simplify control flow of parsing laces

Up until now, when an error happened in one of the inner loops in
matroska_parse_laces, a variable designated for the return value has
been set to an error value and break has been used to exit the
current loop/case. This was done so that the end of matroska_parse_laces
is reached, because said function allocated memory which is later used
and freed in the calling function and passed at the end of
matroska_parse_laces.

But given that there is no allocation any more, one can now return
immediately. And this commit does this.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>