mkv: fix memleak

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/demux/mkv/matroska_segment_parse.cpp

@@ -1005,7 +1005,10 @@ void matroska_segment_c::ParseAttachments( KaxAttachments *attachments )
     while( attachedFile && ( attachedFile->GetSize() > 0 ) )
     {
         KaxFileData  &img_data     = GetChild<KaxFileData>( *attachedFile );
-        attachment_c *new_attachment = new attachment_c( ToUTF8( UTFstring( GetChild<KaxFileName>( *attachedFile ) ) ),
+        char *psz_tmp_utf8 =  ToUTF8( UTFstring( GetChild<KaxFileName>( *attachedFile ) ) );
+        std::string attached_filename(psz_tmp_utf8);
+        free(psz_tmp_utf8);
+        attachment_c *new_attachment = new attachment_c( attached_filename,
                                                         GetChild<KaxMimeType>( *attachedFile ),
                                                         img_data.GetSize() );