Invalidate IPWL_FocusHandler and IPWL_Provider on destruction.

fpdfsdk/src/formfiller/FFL_FormFiller.cpp

Index: fpdfsdk/src/formfiller/FFL_FormFiller.cpp
diff --git a/fpdfsdk/src/formfiller/FFL_FormFiller.cpp b/fpdfsdk/src/formfiller/FFL_FormFiller.cpp
index 2e73b491c93c284da7c59d1ad720abfc4eb8f9f5..ce73f7d4cba00ada80a43d93fbaabbb6ce182d44 100644
--- a/fpdfsdk/src/formfiller/FFL_FormFiller.cpp
+++ b/fpdfsdk/src/formfiller/FFL_FormFiller.cpp
@@ -24,9 +24,10 @@ CFFL_FormFiller::CFFL_FormFiller(CPDFDoc_Environment* pApp,
 }
 
 CFFL_FormFiller::~CFFL_FormFiller() {
-  for (auto& it : m_Maps) {
+  for (const auto& it : m_Maps) {
     CPWL_Wnd* pWnd = it.second;
     CFFL_PrivateData* pData = (CFFL_PrivateData*)pWnd->GetAttachedData();
+    pWnd->InvalidateProvider(this);
     pWnd->Destroy();
     delete pWnd;
     delete pData;