set CardLayout fill_empty=False for add cards editor

Card layout view functions as a previewer in add cards dialog
so displaying accurately is more important than having placeholders.
Especially for card layouts using conditional-not fields {{^Field}}
card layout is rendered badly.

qt/aqt/editor.py

@@ -343,7 +343,7 @@ $editorToolbar.then(({{ toolbar }}) => toolbar.appendGroup({{
             self.note,
             ord=ord,
             parent=self.parentWindow,
-            fill_empty=self.addMode,
+            fill_empty=False,
         )
         if isWin:
             self.parentWindow.activateWindow()