Move mo.melee assignment to BS_PRETURN

mo.melee doesn't really have many justifications for being set every frame. Baton Passing and calling Analysis do not edit mo.melee but were listed as reasons for why it was there. This should allow mods that decide to edit a characters mo.melee attack during BS_DOTURN to do so without resorting to a desync prone alternative of editing the characters charStats table, which also poses problems in multi-party situations where the same character in different parties are acting at the same time.