Fix a bug in https://crrev.com/c/1272937, where event.target can be still null

Fix a bug in the previous CL, https://crrev.com/c/1272937, where event.target
can be null when GetElement() returns nullptr.

Bug: 892970, 893449, 902287
Change-Id: I7a08227d39117c2dc90fe720f0d6ffd62d9b2ea6
Reviewed-on: https://chromium-review.googlesource.com/c/1322177
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606884}

third_party/blink/renderer/modules/accessibility/ax_object.cc

@@ -1095,12 +1095,11 @@ bool AXObject::DispatchEventToAOMEventListeners(Event& event) {
   // that if it didn't previously exist it won't be part of the event path.
   AccessibleNode* target = GetAccessibleNode();
   if (!target) {
-    if (Element* element = GetElement()) {
+    if (Element* element = GetElement())
       target = element->accessibleNode();
-      if (!target)
-        return false;
-    }
   }
+  if (!target)
+    return false;
   event.SetTarget(target);
 
   // Capturing phase.