Code change to avoid signed/unsigned mismatch warnings

fpdfsdk/javascript/PublicMethods.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/PublicMethods.h"
 
 #include <algorithm>
 #include <string>
@@ skipping 1484 matching lines @@
       pEvent->Rc() = FALSE;
     }
     return TRUE;
   }
 
   CFX_WideString& wideChange = pEvent->Change();
   std::wstring wChange = wideChange.c_str();
   if (wChange.empty())
     return TRUE;
 
-  int iIndexMask = pEvent->SelStart();
+  size_t iIndexMask = pEvent->SelStart();
 
   size_t combined_len = wstrValue.length() + wChange.length() -
                         (pEvent->SelEnd() - pEvent->SelStart());
   if (combined_len > wstrMaskLen) {
     Alert(pContext,
           JSGetStringFromID(pContext, IDS_STRING_JSPARAM_TOOLONG).c_str());
     pEvent->Rc() = FALSE;
     return TRUE;
   }
 
@@ skipping 359 matching lines @@
     nums.SetElement(nIndex, CJS_Value(pRuntime, sPart.c_str()));
   }
 
   if (nums.GetLength() > 0)
     vRet = nums;
   else
     vRet.SetNull();
 
   return TRUE;
 }