taglib: add missing vlc_input_attachment_New() error handling

modules/meta_engine/taglib.cpp

@@ -654,10 +654,13 @@ 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() );
-        TAB_APPEND_CAST( (input_attachment_t**),
-                         p_demux_meta->i_attachments, p_demux_meta->attachments,
-                         p_attachment );
-        vlc_meta_SetArtURL( p_meta, "attachment://cover" );
+        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