Add guards for field operations in RmlUi mode

Fixed more editor errors when fields don't have Chili methods:

Editor.lua fixes:
- _AddField: Guard against nil field or missing field.name
- Set: Guard against nil field, make Set() method optional
- Update: Make Update() method optional (only exists on Chili fields)

object_property_window.lua fix:
- Guard stackPanel access when bridge is nil

These changes allow editors to work with simple field tables in RmlUi mode:
- Fields can be added without Chili methods
- editor:Set() works with both Chili fields and plain tables
- editor:Update() doesn't crash on plain field tables
- No more crashes when editors instantiate

Author: claude

scen_edit/view/editor.lua

@@ -360,6 +360,10 @@ function Editor:AddField(field)
 end
 
 function Editor:_AddField(field)
+    if not field or not field.name then
+        Log.Error("Attempted to add field without name")
+        return
+    end
     self.fields[field.name] = field
     field.ev = self
 end
@@ -416,13 +420,26 @@ end
 -- self:Set("myNumber", 15)
 function Editor:Set(name, value)
     local field = self.fields[name]
-    field:Set(value)
+    if not field then
+        Log.Warning("Attempted to set non-existent field: " .. tostring(name))
+        return
+    end
+    -- Only call Set if the method exists (Chili fields)
+    if field.Set then
+        field:Set(value)
+    else
+        -- For RmlUi fields, just set the value directly
+        field.value = value
+    end
 end
 function Editor:Update(name, _source)
     local field = self.fields[name]
     assert(field, "No such field to update: " .. tostring(name))
 
-    field:Update(_source)
+    -- Only call Update if the method exists (Chili fields)
+    if field.Update then
+        field:Update(_source)
+    end
 
     -- update listeners and current state
     if not self.__initializing then

scen_edit/view/object/object_property_window.lua

@@ -568,8 +568,10 @@ function ObjectPropertyWindow:OnSelectionChanged()
     end
 
     if not bridge then
-        self.stackPanel:EnableRealign()
-        self.stackPanel:Invalidate()
+        if self.stackPanel then
+            self.stackPanel:EnableRealign()
+            self.stackPanel:Invalidate()
+        end
         return
     end