Get rid of NULLs in fpdfsdk/

fpdfsdk/pdfwindow/PWL_Wnd.cpp

Index: fpdfsdk/pdfwindow/PWL_Wnd.cpp
diff --git a/fpdfsdk/pdfwindow/PWL_Wnd.cpp b/fpdfsdk/pdfwindow/PWL_Wnd.cpp
index 310f2f3f900b6cc11902ff6eb2e6c2fafc437fa5..2a0a0aabbbf244730500331967d974383e84bdbd 100644
--- a/fpdfsdk/pdfwindow/PWL_Wnd.cpp
+++ b/fpdfsdk/pdfwindow/PWL_Wnd.cpp
@@ -55,7 +55,7 @@ void CPWL_Timer::TimerProc(int32_t idEvent) {
     pTimer->m_pAttached->TimerProc();
 }
 
-CPWL_TimerHandler::CPWL_TimerHandler() : m_pTimer(NULL) {}
+CPWL_TimerHandler::CPWL_TimerHandler() : m_pTimer(nullptr) {}
 
 CPWL_TimerHandler::~CPWL_TimerHandler() {
   delete m_pTimer;
@@ -90,8 +90,8 @@ class CPWL_MsgControl {
   void Default() {
     m_aMousePath.RemoveAll();
     m_aKeyboardPath.RemoveAll();
-    m_pMainMouseWnd = NULL;
-    m_pMainKeyboardWnd = NULL;
+    m_pMainMouseWnd = nullptr;
+    m_pMainKeyboardWnd = nullptr;
   }
 
   FX_BOOL IsWndCreated(const CPWL_Wnd* pWnd) const {
@@ -149,7 +149,7 @@ class CPWL_MsgControl {
       if (CPWL_Wnd* pWnd = m_aKeyboardPath.GetAt(0))
         pWnd->OnKillFocus();
 
-    m_pMainKeyboardWnd = NULL;
+    m_pMainKeyboardWnd = nullptr;
     m_aKeyboardPath.RemoveAll();
   }
 
@@ -168,7 +168,7 @@ class CPWL_MsgControl {
   }
 
   void ReleaseCapture() {
-    m_pMainMouseWnd = NULL;
+    m_pMainMouseWnd = nullptr;
     m_aMousePath.RemoveAll();
   }
 
@@ -181,7 +181,7 @@ class CPWL_MsgControl {
 };
 
 CPWL_Wnd::CPWL_Wnd()
-    : m_pVScrollBar(NULL),
+    : m_pVScrollBar(nullptr),
       m_rcWindow(),
       m_rcClip(),
       m_bCreated(FALSE),
@@ -255,7 +255,7 @@ void CPWL_Wnd::Destroy() {
       if (CPWL_Wnd* pChild = m_aChildren[i]) {
         pChild->Destroy();
         delete pChild;
-        pChild = NULL;
+        pChild = nullptr;
       }
     }
 
@@ -268,7 +268,7 @@ void CPWL_Wnd::Destroy() {
 
   FXSYS_memset(&m_sPrivateParam, 0, sizeof(PWL_CREATEPARAM));
   m_aChildren.RemoveAll();
-  m_pVScrollBar = NULL;
+  m_pVScrollBar = nullptr;
 }
 
 void CPWL_Wnd::Move(const CFX_FloatRect& rcNew,
@@ -624,7 +624,7 @@ CPWL_ScrollBar* CPWL_Wnd::GetVScrollBar() const {
   if (HasFlag(PWS_VSCROLL))
     return m_pVScrollBar;
 
-  return NULL;
+  return nullptr;
 }
 
 void CPWL_Wnd::CreateScrollBar(const PWL_CREATEPARAM& cp) {
@@ -958,7 +958,7 @@ const CPWL_Wnd* CPWL_Wnd::GetFocused() const {
     return pMsgCtrl->m_pMainKeyboardWnd;
   }
 
-  return NULL;
+  return nullptr;
 }
 
 void CPWL_Wnd::EnableWindow(FX_BOOL bEnable) {