Revert "matroskadec: forward parsing errors to caller."

This reverts commit 5dd514af937ff4d74c3c263e4ca428b14b62d5f1.
Silently ignoring errors allows some broken files to simply be played, instead of failing.
(cherry picked from commit 7804b0693375c1a7ba1046f7a3579e9f63c2b15a)

The intended goal (as confirmed with its author) of fixing a crash has been
fixed differently prior to the application of this patch and this patch does
notsucessfully propagate parse errors either.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
