[FIX] gamification, website_profile : re-fix division by zero if user has no karma

If a new user try to access the elearning platform or his porfile, if he has
no karma, has it is the case for new users, he won't get any rank. So that
the next rank karma minus current rank karma equals zero.

To avoid this, next_rank will always be first one existing if the user has no
karma. Also, the current rank will not be displayed if the user has no karma.
finally, next rank will not be displayed if the user reached the last existing
rank.

Task ID : 1941250
PR #31512