Reset the timestamp state on BLOCK_FLAG_DISCONTINUITY.

 On such flag, the bitstream before and after it are not related at all and
so are the timestamp. In order to not confuse the core, do not output
wrong timestamps.

modules/codec/schroedinger.c

@@ -303,6 +303,7 @@ static picture_t *DecodeBlock( decoder_t *p_dec, block_t **pp_block )
         if( p_block->i_flags & BLOCK_FLAG_DISCONTINUITY ) {
             schro_decoder_reset( p_sys->p_schro );
 
+            p_sys->i_lastpts = -1;
             block_Release( p_block );
             *pp_block = NULL;
             return NULL;