taglib: add missing vlc_input_attachment_New() error handling

modules/meta_engine/taglib.cpp

@@ -654,11 +654,14 @@ static void ReadMetaFromMP4( MP4::Tag* tag, demux_meta_t *p_demux_meta, vlc_meta
         input_attachment_t *p_attachment =
                 vlc_input_attachment_New( "cover", psz_format, "cover",
                                           list[0].data().data(), list[0].data().size() );
+        if( p_attachment )
+        {
             TAB_APPEND_CAST( (input_attachment_t**),
                              p_demux_meta->i_attachments, p_demux_meta->attachments,
                              p_attachment );
             vlc_meta_SetArtURL( p_meta, "attachment://cover" );
         }
+    }
 }
 #endif