Attempt StringIO after failed BytesIO file read

This is a bandaid to allow the --input-url option to be used to read in single files. It adds zero functionality beyond what already existed when the --input-file option was used.

requested review from @erigler

assigned to @swilbur

Closing this merge request and awaiting new one from https://code.usgs.gov/ghsc/users/swilbur/geomag-algorithms.

closed