Better error message when script 2 runs out of data

[uniomni]

('data_directory', '/home/petar/media/petar/TOSHIBA EXT/PyARR-data/1%AEP/')
('proc_directory', '/home/petar/media/petar/TOSHIBA
EXT/PyARR-postprocessed-data/1%AEP/')
Postprocessing storm 1 for quantity WL at all specified locations
Traceback (most recent call last):
File "2_critical_duration_patterns.py", line 17, in
points_dict = post_process(durations=durations, locations=locations,
storm=storm, quantity=quantity, proc_directory=proc_directory,
blockage=blockage)
File "/home/petar/PyARR/ARR2019_post_processing.py", line 198, in
post_process
points_dict = critical_duration_pattern(fromdir, locations)
File "/home/petar/PyARR/ARR2019_post_processing.py", line 142, in
critical_duration_pattern
mean, (one_up_filename, value) = find_average_element(filename_list)
File "/home/petar/PyARR/ARR2019_post_processing.py", line 68, in
find_average_element
raise BaseException('Got an empty list: %s' % filename_list)
BaseException: Got an empty list: []