Gracefully handle a disconnected popup menu client on disposing open popup.

Source/web/PopupMenuImpl.cpp

Index: Source/web/PopupMenuImpl.cpp
diff --git a/Source/web/PopupMenuImpl.cpp b/Source/web/PopupMenuImpl.cpp
index a0bc7f3a071538c636edb21991210492a2d31dba..40695b68b55de2c611d95c69a6b4d42226d3ba14 100644
--- a/Source/web/PopupMenuImpl.cpp
+++ b/Source/web/PopupMenuImpl.cpp
@@ -234,11 +234,12 @@ void PopupMenuImpl::setValue(const String& value)
 
 void PopupMenuImpl::didClosePopup()
 {
-    if (m_indexToSetOnClose >= 0)
+    if (m_client && m_indexToSetOnClose >= 0)
         m_client->valueChanged(m_indexToSetOnClose);
     m_indexToSetOnClose = -1;
     m_popup = nullptr;
-    m_client->popupDidHide();
+    if (m_client)
+        m_client->popupDidHide();
 }
 
 Element& PopupMenuImpl::ownerElement()