Getting rid of more (FX_LPCWSTR) casts and fixing two bugs revealed by this.

core/src/fxcrt/fx_basic_wstring.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/fxcrt/fx_basic.h"
 #include "../../../third_party/numerics/safe_math.h"
 
 static CFX_StringDataW* FX_AllocStringW(int nLen)
@@ skipping 568 matching lines @@
         return;
     }
     FXSYS_wcsupr(m_pData->m_String);
 }
 FX_STRSIZE CFX_WideString::Find(FX_LPCWSTR lpszSub, FX_STRSIZE nStart) const
 {
     FX_STRSIZE nLength = GetLength();
     if (nLength < 1 || nStart > nLength) {
         return -1;
     }
-    FX_LPCWSTR lpsz = (FX_LPCWSTR)FXSYS_wcsstr(m_pData->m_String + nStart, lpszSub);
+    FX_LPCWSTR lpsz = FXSYS_wcsstr(m_pData->m_String + nStart, lpszSub);
     return (lpsz == NULL) ? -1 : (int)(lpsz - m_pData->m_String);
 }
 FX_STRSIZE CFX_WideString::Find(FX_WCHAR ch, FX_STRSIZE nStart) const
 {
     if (m_pData == NULL) {
         return -1;
     }
     FX_STRSIZE nLength = m_pData->m_nDataLength;
     if (nStart >= nLength) {
         return -1;
     }
-    FX_LPCWSTR lpsz = (FX_LPCWSTR)FXSYS_wcschr(m_pData->m_String + nStart, ch);
+    FX_LPCWSTR lpsz = FXSYS_wcschr(m_pData->m_String + nStart, ch);
     return (lpsz == NULL) ? -1 : (int)(lpsz - m_pData->m_String);
 }
 void CFX_WideString::TrimRight(FX_LPCWSTR lpszTargetList)
 {
     FXSYS_assert(lpszTargetList != NULL);
     if (m_pData == NULL || *lpszTargetList == 0) {
         return;
     }
     CopyBeforeWrite();
     FX_STRSIZE len = GetLength();
@@ skipping 508 matching lines @@
             return (CFX_CharMap*)&g_DefaultJISMapper;
         case 936:
             return (CFX_CharMap*)&g_DefaultGBKMapper;
         case 949:
             return (CFX_CharMap*)&g_DefaultUHCMapper;
         case 950:
             return (CFX_CharMap*)&g_DefaultBig5Mapper;
     }
     return NULL;
 }