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 975385fb29c2078402f9cd2ff0b0c69781e6e0ad..61807ee93fefb3ae8424c23dfa85d7306c07b7cf 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;