[om_account_followup/report/followup_print.py] fix for TypeError: '<=' not supported between instances of 'datetime.date' and 'str'

[tilleul]

FYI; there's a bug in this file for versions 14, 15 & 16 ...

Code from version 14 (line 239-240) reads:

elif date and date <= fups[followup_line_id][0].strftime(
                    '%Y-%m-%d'):

But it should be

elif date and fields.Date.to_string(date) <= fups[followup_line_id][0].strftime(
                    '%Y-%m-%d'):

otherwise you get the error message mentioned in the title of this post.

Other versions have the same line in the same file but in different locations.