fix the no existing space weather file exception.

This work is a proposal regarding fixing the polaris issue 132.

Changes :

The ftplib.error_perm exception in the sw_file_fetch.py file is now catched. When this happens we remove the empty created file and the file name from the list that is passed to the method extract_data_from_multiple for extraction.

How to reproduce the issue from polaris :

Just run this code :

from vinvelivaanilai.space_weather.sw_file_fetch import fetch_indices
import datetime

start_date = datetime.datetime(year=2019, month=2, day=18)
end_date = datetime.datetime(year=2021, month=3, day=7)
fetch_indices("DPD", start_date, end_date)