Clean up XFA code which causes warnings

xfa/fxfa/app/xfa_ffwidgetacc.cpp

Index: xfa/fxfa/app/xfa_ffwidgetacc.cpp
diff --git a/xfa/fxfa/app/xfa_ffwidgetacc.cpp b/xfa/fxfa/app/xfa_ffwidgetacc.cpp
index 08c52de79aa4ffc166381a65302ab1136884c06c..2c84a7f9b7489cda85cdfcf9046d8167158f725f 100644
--- a/xfa/fxfa/app/xfa_ffwidgetacc.cpp
+++ b/xfa/fxfa/app/xfa_ffwidgetacc.cpp
@@ -713,7 +713,7 @@ CXFA_FFWidget* CXFA_WidgetAcc::GetNextWidget(CXFA_FFWidget* pWidget) {
 }
 void CXFA_WidgetAcc::UpdateUIDisplay(CXFA_FFWidget* pExcept) {
   CXFA_FFWidget* pWidget = NULL;
-  while ((pWidget = GetNextWidget(pWidget))) {
+  while ((pWidget = GetNextWidget(pWidget)) != nullptr) {

[Lei Zhang, 2016/05/20 03:48:02]

Why do we need the explicit check against nullptr?

[Wei Li, 2016/05/20 16:33:15]

This is due to msvs warning c4706 "assignment within conditional expression".
The warning prevents people accidentally write "if (a=b)" instead of "if(a==b)".
 

     if (pWidget == pExcept || !pWidget->IsLoaded() ||
         (GetUIType() != XFA_ELEMENT_CheckButton && pWidget->IsFocused())) {
       continue;