Avoid a crash if there are duplicated files in dir

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit 934582e46d03f2acdb39b170b161856c42db61b7)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/demux/mkv/demux.cpp

@@ -528,10 +528,10 @@ matroska_stream_c *demux_sys_t::AnalyseAllSegmentsFound( demux_t *p_demux, EbmlS
                         {
                             KaxSegmentUID *p_uid = static_cast<KaxSegmentUID*>(l);
                             b_keep_segment = (FindSegment( *p_uid ) == NULL);
-                            if ( !b_keep_segment )
-                                break; // this segment is already known
                             delete p_segment1->p_segment_uid;
                             p_segment1->p_segment_uid = new KaxSegmentUID(*p_uid);
+                            if ( !b_keep_segment )
+                                break; // this segment is already known
                         }
                         else if( MKV_IS_ID( l, KaxPrevUID ) )
                         {