fix chaos boss shuffle in mystery being vanilla, and prevent that mistake in the future

Bosses.py

@@ -252,3 +252,5 @@ def place_bosses(world, player: int):
                 can_place_boss(world, player, boss, loc, level) for loc, level in remaining_boss_locations)])
             for loc, level in remaining_boss_locations:
                 place_boss(world, player, remaining_boss, loc, level)
+    else:
+        raise FillError(f"Could not find boss shuffle mode {world.boss_shuffle[player]}")

Mystery.py

@@ -337,7 +337,7 @@ def roll_settings(weights):
     ret.shufflebosses = {'none': 'none',
                          'simple': 'basic',
                          'full': 'normal',
-                         'random': 'random',
+                         'random': 'chaos',
                          'singularity': 'singularity',
                          'duality': 'singularity'
                          }[get_choice('boss_shuffle', weights)]