Make conversion to CPDF_Dest explicit

core/include/fpdfdoc/fpdf_doc.h

Index: core/include/fpdfdoc/fpdf_doc.h
diff --git a/core/include/fpdfdoc/fpdf_doc.h b/core/include/fpdfdoc/fpdf_doc.h
index dbcc7f433e08546e99f764edb36fedf1525d0699..dac215e711b10dc3733d6dfea41b419195a38395 100644
--- a/core/include/fpdfdoc/fpdf_doc.h
+++ b/core/include/fpdfdoc/fpdf_doc.h
@@ -124,28 +124,19 @@ public:
 class CPDF_Dest : public CFX_Object
 {
 public:
+    CPDF_Dest() : m_pObj(nullptr) { }
+    explicit CPDF_Dest(CPDF_Object* pObj) : m_pObj(pObj) { }
 
-    CPDF_Dest(CPDF_Object* pObj = NULL)
-    {
-        m_pObj = pObj;
-    }
-
-    operator CPDF_Object* () const
-    {
-        return m_pObj;
-    }
+    operator bool () const { return m_pObj != NULL; }
+    CPDF_Object* GetObject() const { return m_pObj; }
 
     CFX_ByteString		GetRemoteName();
-
     int					GetPageIndex(CPDF_Document* pDoc);
-
     FX_DWORD			GetPageObjNum();
-
     int					GetZoomMode();
-
     FX_FLOAT			GetParam(int index);
 
-
+protected:
     CPDF_Object*		m_pObj;
 };
 class CPDF_OCContext : public CFX_Object, public IPDF_OCContext