List index out of range exception in get_adc_offsets

[csatt]

If the adc_pairs_yymmdd_hh_mm_ss.csv file is corrupted such that there are fewer than two points, an exception is detected in get_adc_offsets:

IndexError: list index out of range

This would also occur for any other (anomalous) case where the adc_pairs list has fewer than two points.

The process_adc_values() method should check the length of the adc_pairs list to make sure it has at least two points to prevent this exception.