Invalidate IPWL_FocusHandler and IPWL_Provider on destruction.

fpdfsdk/src/pdfwindow/PWL_Wnd.cpp

Index: fpdfsdk/src/pdfwindow/PWL_Wnd.cpp
diff --git a/fpdfsdk/src/pdfwindow/PWL_Wnd.cpp b/fpdfsdk/src/pdfwindow/PWL_Wnd.cpp
index 9c4e21713b8e7fc5b73daa86681f2e7032d35977..5bedad127a3375cace5fc837d79eba96dd9d777d 100644
--- a/fpdfsdk/src/pdfwindow/PWL_Wnd.cpp
+++ b/fpdfsdk/src/pdfwindow/PWL_Wnd.cpp
@@ -237,6 +237,16 @@ void CPWL_Wnd::OnCreated() {}
 
 void CPWL_Wnd::OnDestroy() {}
 
+void CPWL_Wnd::InvalidateFocusHandler(IPWL_FocusHandler* handler) {
+  if (m_sPrivateParam.pFocusHandler == handler)
+    m_sPrivateParam.pFocusHandler = nullptr;
+}
+
+void CPWL_Wnd::InvalidateProvider(IPWL_Provider* provider) {
+  if (m_sPrivateParam.pProvider == provider)
+    m_sPrivateParam.pProvider = nullptr;
+}
+
 void CPWL_Wnd::Destroy() {
   KillFocus();