[orca] Handle another object going defunct on us

[Joanmarie Diggs <joanied src gnome org>]

commit 567dd57fbe45d693ee1b271b652951ca86306500
Author: Joanmarie Diggs <jdiggs igalia com>
Date:   Mon Apr 27 18:52:12 2020 -0400

    Handle another object going defunct on us

 src/orca/scripts/toolkits/Chromium/script_utilities.py | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/src/orca/scripts/toolkits/Chromium/script_utilities.py 
b/src/orca/scripts/toolkits/Chromium/script_utilities.py
index 1688f1c11..fe37b3f63 100644
--- a/src/orca/scripts/toolkits/Chromium/script_utilities.py
+++ b/src/orca/scripts/toolkits/Chromium/script_utilities.py
@@ -320,6 +320,9 @@ class Utilities(web.Utilities):
         if obj.getRole() == pyatspi.ROLE_LIST_ITEM:
             listbox = listbox.parent
 
+        if not listbox:
+            return result
+
         # The listbox sometimes claims to be a redundant object rather than a listbox.
         # Clearing the AT-SPI2 cache seems to be the trigger.
         if not (listbox and listbox.getRole() in roles):