Prevent cloned arrays/dictionaries from having nullptrs.

core/fpdfapi/fpdf_parser/cpdf_dictionary.cpp

Index: core/fpdfapi/fpdf_parser/cpdf_dictionary.cpp
diff --git a/core/fpdfapi/fpdf_parser/cpdf_dictionary.cpp b/core/fpdfapi/fpdf_parser/cpdf_dictionary.cpp
index 27b866a65b52010ba06179754904013faec75448..8e4b282ef96a4a52e2d628f3ff8a7c0c84b19767 100644
--- a/core/fpdfapi/fpdf_parser/cpdf_dictionary.cpp
+++ b/core/fpdfapi/fpdf_parser/cpdf_dictionary.cpp
@@ -46,8 +46,11 @@ const CPDF_Dictionary* CPDF_Dictionary::AsDictionary() const {
 
 CPDF_Object* CPDF_Dictionary::Clone(FX_BOOL bDirect) const {
   CPDF_Dictionary* pCopy = new CPDF_Dictionary();
-  for (const auto& it : *this)
-    pCopy->m_Map.insert(std::make_pair(it.first, it.second->Clone(bDirect)));
+  for (const auto& it : *this) {
+    CPDF_Object* pClonedObj = it.second->Clone(bDirect);
+    if (pClonedObj)
+      pCopy->m_Map.insert(std::make_pair(it.first, pClonedObj));
+  }
   return pCopy;
 }