apedec: set s->samples only when init_frame_decoder succeeded

Otherwise range_start_decoding is not necessarily run and thus
ctx->rc.range still 0 in range_dec_normalize leading to an infinite
loop.

Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
