Bug 1779975: Check whether a LocalAccessible has its own content before trying to get MarkupMapInfo from it. r=eeejay

Differential Revision: https://phabricator.services.mozilla.com/D152254

accessible/base/nsAccessibilityService.cpp

@@ -1665,7 +1665,9 @@ void nsAccessibilityService::NotifyOfConsumersChange() {
 const mozilla::a11y::MarkupMapInfo* nsAccessibilityService::GetMarkupMapInfoFor(
     Accessible* aAcc) const {
   if (LocalAccessible* localAcc = aAcc->AsLocal()) {
-    return GetMarkupMapInfoFor(localAcc->GetContent());
+    return localAcc->HasOwnContent()
+               ? GetMarkupMapInfoFor(localAcc->GetContent())
+               : nullptr;
   }
   // XXX For now, we assume all RemoteAccessibles are HTML elements. This
   // isn't strictly correct, but as far as current callers are concerned,