return the last comment.
Retrieve the quality control record for the named pngwalk image. It is assumed that the previously saved record, if there is one, exists in the same folder as the image. If a saved record is not found, a new one will be created.
Retrieve the quality control record for the named pngwalk image. If qcFolder
is non-null, it should point to a folder that already exists and contains any saved quality
control records; if it is null, the records are assumed to be saved in the same folder as the images.
Set the "new" commentText on this record. This commentText will be appended to the existing list of comments when the record is written.