bee rewards doesn't store best score on selecting the best goal

3iff reported a bug in main.nut: https://www.tt-forums.net/viewtopic.php?p=1222592#p1222592

Bug found in Busy Bee and Bee Rewards v5892

Main.nut line 260.

It reads prod_score = best_score; but that's actually backwards. It should read best_score = prod_score;

That way, it actually records the best score. At the moment it just selects the last non-zero score and uses that as the goal destination.