Re-enable several MSVC warnings

fpdfsdk/javascript/Document.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "fpdfsdk/javascript/Document.h"
 
 #include <vector>
 
@@ skipping 1441 matching lines @@
 
   int nWords = 0;
 
   CPDF_Font* pFont = pTextObj->GetFont();
   if (!pFont)
     return 0;
 
   FX_BOOL bIsLatin = FALSE;
 
   for (int i = 0, sz = pTextObj->CountChars(); i < sz; i++) {
-    FX_DWORD charcode = -1;
+    FX_DWORD charcode = static_cast<FX_DWORD>(-1);
     FX_FLOAT kerning;
 
     pTextObj->GetCharInfo(i, charcode, kerning);
     CFX_WideString swUnicode = pFont->UnicodeFromCharCode(charcode);
 
     FX_WORD unicode = 0;
     if (swUnicode.GetLength() > 0)
       unicode = swUnicode[0];
 
     if (ISLATINWORD(unicode) && bIsLatin)
@@ skipping 12 matching lines @@
   CFX_WideString swRet;
 
   CPDF_Font* pFont = pTextObj->GetFont();
   if (!pFont)
     return L"";
 
   int nWords = 0;
   FX_BOOL bIsLatin = FALSE;
 
   for (int i = 0, sz = pTextObj->CountChars(); i < sz; i++) {
-    FX_DWORD charcode = -1;
+    FX_DWORD charcode = static_cast<FX_DWORD>(-1);
     FX_FLOAT kerning;
 
     pTextObj->GetCharInfo(i, charcode, kerning);
     CFX_WideString swUnicode = pFont->UnicodeFromCharCode(charcode);
 
     FX_WORD unicode = 0;
     if (swUnicode.GetLength() > 0)
       unicode = swUnicode[0];
 
     if (ISLATINWORD(unicode) && bIsLatin) {
@@ skipping 89 matching lines @@
     }
   }
 
   for (const auto& pData : DelayDataForFieldAndControlIndex)
     Field::DoDelay(m_pDocument, pData.get());
 }
 
 CJS_Document* Document::GetCJSDoc() const {
   return static_cast<CJS_Document*>(m_pJSObject);
 }