Malformed priority files crash schedule_single_station.py

Typical error message (reported this forum post):

Traceback (most recent call last):
File “./schedule_single_station.py”, line 292, in
main()
File “./schedule_single_station.py”, line 230, in main
priorities, favorite_transmitters = read_priorities_transmitters(priority_filename)
File “/usr/local/bin/satnogs-auto-scheduler/utils.py”, line 20, in read_priorities_transmitters
prio = parts[1]
IndexError: list index out of range

Fix already available in !57 (merged).