fixed randomizer container UI bug

com.unity.perception/Editor/Randomization/Uxml/Randomizer/RandomizerList.uxml

 <UXML xmlns="UnityEngine.UIElements">
-    <VisualElement name="randomizers-container" class="scenario__dark-viewport" style="margin-top: 6px; min-height: 100px;"/>
-    <VisualElement style="flex-direction: row; align-items: center; justify-content: center; margin-top: 4px;">
-        <Button name="add-randomizer-button" text="Add Randomizer"/>
-        <Button name="expand-all" text="Expand All"/>
-        <Button name="collapse-all" text="Collapse All"/>
+    <VisualElement style="min-height: 132px;">
+        <VisualElement name="randomizers-container" class="scenario__dark-viewport" style="margin-top: 6px; min-height: 100px;"/>
+        <VisualElement style="flex-direction: row; align-items: center; justify-content: center; margin-top: 4px;">
+            <Button name="add-randomizer-button" text="Add Randomizer"/>
+            <Button name="expand-all" text="Expand All"/>
+            <Button name="collapse-all" text="Collapse All"/>
+        </VisualElement>
     </VisualElement>
 </UXML>

com.unity.perception/Editor/Randomization/VisualElements/Randomizer/AddRandomizerMenu.cs

         {
             var rootList = new List<MenuItem>();
             m_MenuItemsMap.Add(string.Empty, rootList);
+
+            var randomizerTypeSet = new HashSet<Type>();
+            foreach (var randomizer in m_RandomizerList.scenario.m_Randomizers)
+                randomizerTypeSet.Add(randomizer.GetType());
+
-                if (m_RandomizerList.randomizerTypeSet.Contains(randomizerType))
+                if (randomizerTypeSet.Contains(randomizerType))
                     continue;
                 var menuAttribute = (AddRandomizerMenuAttribute)Attribute.GetCustomAttribute(randomizerType, typeof(AddRandomizerMenuAttribute));
                 if (menuAttribute != null)

com.unity.perception/Editor/Randomization/VisualElements/Randomizer/RandomizerList.cs

     {
         SerializedProperty m_Property;
         VisualElement m_Container;
-        ToolbarMenu m_AddRandomizerMenu;
-        public HashSet<Type> randomizerTypeSet = new HashSet<Type>();
-        ScenarioBase scenario => (ScenarioBase)m_Property.serializedObject.targetObject;
+        public ScenarioBase scenario => (ScenarioBase)m_Property.serializedObject.targetObject;
 
         VisualElement inspectorContainer
         {
             m_Container.Clear();
             for (var i = 0; i < m_Property.arraySize; i++)
                 m_Container.Add(new RandomizerElement(m_Property.GetArrayElementAtIndex(i), this));
-            randomizerTypeSet.Clear();
-            foreach (var randomizer in scenario.randomizers)
-                randomizerTypeSet.Add(randomizer.GetType());
         }
 
         public void AddRandomizer(Type randomizerType)

com.unity.perception/Runtime/Randomization/Scenarios/ScenarioBase.cs

         {
             if (!randomizerType.IsSubclassOf(typeof(Randomizer)))
                 throw new ScenarioException(
-                    $"Cannot add non-randomizer type {randomizerType.Name} to randomizer list");
+                    $"Cannot remove non-randomizer type {randomizerType.Name} from randomizer list");
             var removed = false;
             for (var i = 0; i < m_Randomizers.Count; i++)
             {