Merge to XFA: Add some nullptr checks that were missing from commit f7992b39.

core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp

Index: core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
index e49835496c134a525ca6e6641da3b1ee8a8d7580..e8b300027c813d3050c24e4ccefc2491c5379165 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
@@ -851,7 +851,8 @@ FX_BOOL CPDF_Parser::RebuildCrossRef() {
                           CFX_ByteString key;
                           CPDF_Object* pElement =
                               pTrailer->GetNextElement(pos, key);
-                          FX_DWORD dwObjNum = pElement->GetObjNum();
+                          FX_DWORD dwObjNum =
+                              pElement ? pElement->GetObjNum() : 0;
                           if (dwObjNum) {
                             m_pTrailer->SetAtReference(key, m_pDocument,
                                                        dwObjNum);