Fix potential memory violation in CJS_PublicMethods::StrRTrim()

fpdfsdk/src/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 "../../include/javascript/JavaScript.h"
 #include "../../include/javascript/IJavaScript.h"
 #include "../../include/javascript/JS_Define.h"
 #include "../../include/javascript/JS_Object.h"
@@ skipping 204 matching lines @@
 CFX_WideString CJS_PublicMethods::StrLTrim(FX_LPCWSTR pStr)
 {
         while (*pStr && *pStr == L' ') pStr++;
 
         return pStr;
 }
 
 CFX_WideString CJS_PublicMethods::StrRTrim(FX_LPCWSTR pStr)
 {
         FX_LPCWSTR p = pStr;
+        while (*p) p++;
+        while (p > pStr && *(p - 1) == L' ') p--;
 
-        while (*p) p++;
-        p--;
-        if (p >= pStr)
-        {               
-                while (*p && *p == L' ') p--;
-                p++;
-                return CFX_WideString(pStr,p-pStr);
-        }
-        return L"";
+        return CFX_WideString(pStr, p - pStr);
 }
 
 CFX_WideString CJS_PublicMethods::StrTrim(FX_LPCWSTR pStr)
 {
         return StrRTrim(StrLTrim(pStr));
 }
 
 CFX_ByteString CJS_PublicMethods::StrLTrim(FX_LPCSTR pStr)
 {
         while (*pStr && *pStr == ' ') pStr++;
 
-    return pStr;
+        return pStr;
 }
 
 CFX_ByteString CJS_PublicMethods::StrRTrim(FX_LPCSTR pStr)
 {
         FX_LPCSTR p = pStr;
+        while (*p) p++;
+        while (p > pStr && *(p - 1) == L' ') p--;
 
-        while (*p) p++;
-        p--;
-        if (p >= pStr)
-        {               
-                while (*p && *p == ' ') p--;
-                p++;
-                return CFX_ByteString(pStr,p-pStr);
-        }
-        return "";
+        return CFX_ByteString(pStr,p-pStr);
 }
 
 CFX_ByteString CJS_PublicMethods::StrTrim(FX_LPCSTR pStr)
 {
         return StrRTrim(StrLTrim(pStr));
 }
 
 double CJS_PublicMethods::ParseNumber(FX_LPCWSTR swSource, FX_BOOL& bAllDigits, FX_BOOL& bDot, FX_BOOL& bSign, FX_BOOL& bKXJS)
 {
         bDot = FALSE;
@@ skipping 2055 matching lines @@
                 nums.SetElement(nIndex,CJS_Value(isolate,(FX_LPCWSTR)sPart));   
         }
 
         if (nums.GetLength() > 0)
                 vRet = nums;
         else
                 vRet.SetNull();
 
         return TRUE;
 }