demux: mp4: fix NULL dereference handling trun

modules/demux/mp4/mp4.c

@@ -4562,6 +4562,8 @@ static int LeafParseTRUN( demux_t *p_demux, mp4_track_t *p_track,
             es_out_Control( p_demux->out, ES_OUT_SET_PCR, VLC_TS_0 + i_nzdts );
         }
 
+        if ( p_block )
+        {
             if ( p_track->p_es )
             {
                 p_block->i_dts = VLC_TS_0 + i_nzdts;
@@ -4569,7 +4571,8 @@ static int LeafParseTRUN( demux_t *p_demux, mp4_track_t *p_track,
                 p_block->i_length = CLOCK_FREQ * dur / p_track->i_timescale;
                 MP4_Block_Send( p_demux, p_track, p_block );
             }
-        else free( p_block );
+            else block_Release( p_block );
+        }
 
         chunk_size += len;
     }