Bug 1788547: Null check table acc exists before firing styling changed event, add assert for debugging r=Jamie

Differential Revision: https://phabricator.services.mozilla.com/D156987

accessible/base/nsAccessibilityService.cpp

@@ -568,12 +568,13 @@ void nsAccessibilityService::TableLayoutGuessMaybeChanged(
     PresShell* aPresShell, nsIContent* aContent) {
   if (DocAccessible* document = GetDocAccessible(aPresShell)) {
     if (LocalAccessible* acc = document->GetAccessible(aContent)) {
-      LocalAccessible* table = nsAccUtils::TableFor(acc);
+      if (LocalAccessible* table = nsAccUtils::TableFor(acc)) {
         document->FireDelayedEvent(
             nsIAccessibleEvent::EVENT_TABLE_STYLING_CHANGED, table);
         document->QueueCacheUpdate(table, CacheDomain::Table);
       }
     }
+  }
 }
 
 void nsAccessibilityService::ComboboxOptionMaybeChanged(