Do not dispatch gestures to a NULL aura::Window target

ui/aura/window_event_dispatcher.cc

Index: ui/aura/window_event_dispatcher.cc
diff --git a/ui/aura/window_event_dispatcher.cc b/ui/aura/window_event_dispatcher.cc
index eb08269c95bc94138074385699a928d294916208..f69d7257619d027debb474a1ec2caefe85e42e95 100644
--- a/ui/aura/window_event_dispatcher.cc
+++ b/ui/aura/window_event_dispatcher.cc
@@ -285,6 +285,9 @@ ui::EventDispatchDetails WindowEventDispatcher::ProcessGestures(
     return details;
 
   Window* target = GetGestureTarget(gestures->get().at(0));
+  if (!target)
+    return details;
+
   for (size_t i = 0; i < gestures->size(); ++i) {
     ui::GestureEvent* event = gestures->get().at(i);
     event->ConvertLocationToTarget(window(), target);