Make down-conversion explicit from CFX_Widetring to CFX_WideStringC.

xfa/fxfa/parser/xfa_document_serialize.cpp

Index: xfa/fxfa/parser/xfa_document_serialize.cpp
diff --git a/xfa/fxfa/parser/xfa_document_serialize.cpp b/xfa/fxfa/parser/xfa_document_serialize.cpp
index 2ae82e3c356fc950690ac352d16eb28daef27329..39590f6e8f8c1e4fc9f3fe3a84dfe374bf698cef 100644
--- a/xfa/fxfa/parser/xfa_document_serialize.cpp
+++ b/xfa/fxfa/parser/xfa_document_serialize.cpp
@@ -297,7 +297,7 @@ static void XFA_DataExporter_RegenerateFormFile_Changed(
         buf << FX_WSTRC(L" xmlns=\"\"\n>");
         for (int32_t i = 0; i < wsSelTextArray.GetSize(); i++) {
           buf << FX_WSTRC(L"<value\n>");
-          buf << XFA_ExportEncodeContent(wsSelTextArray[i]);
+          buf << XFA_ExportEncodeContent(wsSelTextArray[i].AsWideStringC());
           buf << FX_WSTRC(L"</value\n>");
         }
         buf << FX_WSTRC(L"</");