Allow FPDFBookmark_GetFirstChild to return the top level bookmark

fpdfsdk/src/fpdfdoc.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/fsdk_define.h"
 #include "../include/fpdfdoc.h"
 
 static int THISMODULE = 0;
@@ skipping 11 matching lines @@
                 CPDF_Bookmark found = FindBookmark(tree, child, title);
                 if (found)
                         return found;
                 child = tree.GetNextSibling(child);
         }
         return CPDF_Bookmark();
 }
 
 DLLEXPORT FPDF_BOOKMARK STDCALL FPDFBookmark_GetFirstChild(FPDF_DOCUMENT document, FPDF_BOOKMARK pDict)
 {
-    if (!document || !pDict)
+    if (!document)
         return NULL;
     CPDF_Document* pDoc = (CPDF_Document*)document;
     CPDF_BookmarkTree tree(pDoc);
     CPDF_Bookmark bookmark = CPDF_Bookmark((CPDF_Dictionary*)pDict);
     return tree.GetFirstChild(bookmark).GetDict();
 }
 
 DLLEXPORT FPDF_BOOKMARK STDCALL FPDFBookmark_GetNextSibling(FPDF_DOCUMENT document, FPDF_BOOKMARK pDict)
 {
     if (!document || !pDict)
@@ skipping 250 matching lines @@
         CFX_ByteString encodedText = text.UTF16LE_Encode();
         unsigned long len = encodedText.GetLength();
         if (buffer && buflen >= len + 2) {
                 FXSYS_memcpy(buffer, encodedText.c_str(), len);
                 // use double zero as trailer
                 ((FX_BYTE*)buffer)[len] = 0;
                 ((FX_BYTE*)buffer)[len + 1] = 0;
         }
         return len+2;
 }