grademax should be reset to 100 when switching from natural agg method to different one

if category with any other than natural agg method is created the grademax is set to 100. When we change the agg method to natural the grademax is adjusted. When we change the agg method from natural to anything else the grademax is NOT set to 100.

P.S. I don't know atm if 100 is hardcoded or is a setting