Handle special blocks in subsdec.

(cherry picked from commit a141e907)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/codec/subtitles/subsdec.c

@@ -259,6 +259,11 @@ static subpicture_t *DecodeBlock( decoder_t *p_dec, block_t **pp_block )
         return NULL;
 
     p_block = *pp_block;
+    if( p_block->i_flags & (BLOCK_FLAG_DISCONTINUITY|BLOCK_FLAG_CORRUPTED) )
+    {
+        block_Release( p_block );
+        return NULL;
+    }
     if( p_block->i_rate != 0 )
         p_block->i_length = p_block->i_length * p_block->i_rate / INPUT_RATE_DEFAULT;