[orca] Chromium: Handle window activate event with null children

[Joanmarie Diggs <joanied src gnome org>]

commit 76396d4b302b32f772941891faa9b2a553da61f5
Author: Joanmarie Diggs <jdiggs igalia com>
Date:   Sun Jun 13 14:45:32 2021 +0200

    Chromium: Handle window activate event with null children

 src/orca/scripts/toolkits/Chromium/script.py | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
---
diff --git a/src/orca/scripts/toolkits/Chromium/script.py b/src/orca/scripts/toolkits/Chromium/script.py
index 653cf1639..62b0198a5 100644
--- a/src/orca/scripts/toolkits/Chromium/script.py
+++ b/src/orca/scripts/toolkits/Chromium/script.py
@@ -353,7 +353,7 @@ class Script(web.Script):
         if super().onTextAttributesChanged(event):
             return
 
-        msg = "Chromium: Passing along event to default script"
+        msg = "CHROMIUM: Passing along event to default script"
         debug.println(debug.LEVEL_INFO, msg, True)
         default.Script.onTextAttributesChanged(self, event)
 
@@ -429,6 +429,11 @@ class Script(web.Script):
         # already showing at the time of window activation. If that changes,
         # we should store presented alerts so we don't double-present them.
         for child in event.source:
+            if not child:
+                msg = "CHROMIUM: Event source claims null child"
+                debug.println(debug.LEVEL_INFO, msg, True)
+                continue
+
             if child.getRole() == pyatspi.ROLE_ALERT:
                 self.presentObject(child)