Change IFWL_Widget to store a single delegate.

xfa/fwl/core/ifwl_combolist.cpp

Index: xfa/fwl/core/ifwl_combolist.cpp
diff --git a/xfa/fwl/core/ifwl_combolist.cpp b/xfa/fwl/core/ifwl_combolist.cpp
index 0fdc5ac6d9973853bf5bc037852ffa5126e69167..91068c3dbde5b8dc4630d944de9190b865e0f219 100644
--- a/xfa/fwl/core/ifwl_combolist.cpp
+++ b/xfa/fwl/core/ifwl_combolist.cpp
@@ -112,8 +112,7 @@ void CFWL_ComboListImpDelegate::OnProcessMessage(CFWL_Message* pMessage) {
       if (rect.Contains(pMsg->m_fx, pMsg->m_fy)) {
         pMsg->m_fx -= rect.left;
         pMsg->m_fy -= rect.top;
-        m_pOwner->m_pVertScrollBar->GetCurrentDelegate()->OnProcessMessage(
-            pMsg);
+        m_pOwner->m_pVertScrollBar->GetDelegate()->OnProcessMessage(pMsg);
         return;
       }
     }