Re-enable several MSVC warnings

fpdfsdk/fpdftext.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 "public/fpdf_text.h"
 
 #include "core/fpdftext/include/ipdf_linkextract.h"
 #include "core/fpdftext/include/ipdf_textpage.h"
@@ skipping 32 matching lines @@
 DLLEXPORT int STDCALL FPDFText_CountChars(FPDF_TEXTPAGE text_page) {
   if (!text_page)
     return -1;
   IPDF_TextPage* textpage = (IPDF_TextPage*)text_page;
   return textpage->CountChars();
 }
 
 DLLEXPORT unsigned int STDCALL FPDFText_GetUnicode(FPDF_TEXTPAGE text_page,
                                                    int index) {
   if (!text_page)
-    return -1;
+    return 0;
   IPDF_TextPage* textpage = (IPDF_TextPage*)text_page;
 
   if (index < 0 || index >= textpage->CountChars())
     return 0;
 
   FPDF_CHAR_INFO charinfo;
   textpage->GetCharInfo(index, &charinfo);
   return charinfo.m_Unicode;
 }
 
@@ skipping 228 matching lines @@
     CFX_FloatRect rect = rectArray.GetAt(rect_index);
     *left = rect.left;
     *right = rect.right;
     *top = rect.top;
     *bottom = rect.bottom;
   }
 }
 DLLEXPORT void STDCALL FPDFLink_CloseWebLinks(FPDF_PAGELINK link_page) {
   delete (IPDF_LinkExtract*)link_page;
 }