sample update with no new samples or colums will fail silently

[antgonza]

This is an issue if we are trying to update the information without adding any new samples or metadata columns. The hack solution is to remove a column and then update the sample info file.

The issue is _common_extend_steps

            if not new_cols and not new_samples:
                return

it should be:

            if not new_cols and not new_samples:
                return None, None

cc: @ackermag