Bug 1688490: Make GetNativeFromGeckoAccessible null-safe r=eeejay

Differential Revision: https://phabricator.services.mozilla.com/D103813

accessible/mac/mozAccessible.h

@@ -27,7 +27,9 @@ namespace a11y {
 
 inline mozAccessible* GetNativeFromGeckoAccessible(
     mozilla::a11y::AccessibleOrProxy aAccOrProxy) {
-  MOZ_ASSERT(!aAccOrProxy.IsNull(), "Cannot get native from null accessible");
+  if (aAccOrProxy.IsNull()) {
+    return nil;
+  }
   if (Accessible* acc = aAccOrProxy.AsAccessible()) {
     mozAccessible* native = nil;
     acc->GetNativeInterface((void**)&native);

accessible/mac/mozSelectableElements.mm

@@ -263,10 +263,12 @@ using namespace mozilla::a11y;
   // we override this method.
   AccessibleOrProxy parentAcc = [parent geckoAccessible];
   if (!parentAcc.IsNull()) {
-    mozAccessible* directGrandparent =
-        GetNativeFromGeckoAccessible(parentAcc.Parent());
-    if ([directGrandparent isKindOfClass:[MOXWebAreaAccessible class]]) {
-      return [parent moxIgnoreWithParent:directGrandparent];
+    AccessibleOrProxy grandparentAcc = parentAcc.Parent();
+    if (mozAccessible* directGrandparent =
+            GetNativeFromGeckoAccessible(grandparentAcc)) {
+      if ([directGrandparent isKindOfClass:[MOXWebAreaAccessible class]]) {
+        return [parent moxIgnoreWithParent:directGrandparent];
+      }
     }
   }