BUGFIX: Circle extraction

The extraction of all data in a circle is based on a heuristic that is not always fulfilled.

See comment in def extract_circle in utils/extraction_tools.py.

The heuristic: If the longitude index is <0, then use the python minus indexing method and use the last values of the data, because of a circle (-180=+180). This is only true, if the data is available for the range +180E to -180W. In all other cases, this leads to wrong results because the gap is skipped and values far away are used.

To correct this, the extract_circle function needs to check, if data is globally or only locally available.