get_status True and missing tags

[kjbrak]

In the case when a tag (e.g. "tag_id") does not exist, tagreader returns a dataframe with a column named "tag-id" and numpy nan values. When get_status=True and a tag does not exist tagreader returns the "tag_id" column with nan values, but not "tag_id::status" with nan values.

This could of course be handled by the code calling tagreader, but I think it makes sense for tagreader to return "tag_id::status" with nan values since this column is expected when get_status=True is used and a missing tag is passed to tagreader.