theora: fix memleak in case of error or discontinuity

Closes #9414

(cherry picked from commit 75946591b91bb1b117d3d1e74081fa709a34315c)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/codec/theora.c

@@ -409,6 +409,7 @@ static void *ProcessPacket( decoder_t *p_dec, ogg_packet *p_oggpacket,
         /* Don't send the the first packet after a discontinuity to
          * theora_decode, otherwise we get purple/green display artifacts
          * appearing in the video output */
+        block_Release(p_block);
         return NULL;
     }