Fix some iterator invalidation issues while traversing CPDF_Dictionary.

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 73da3619bb4ba7dfc8f860db13f327c18f69b6c3..6f0fc76fc02f5fcbf868bdeeaf759dcdbc97752a 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
@@ -885,9 +885,11 @@ FX_BOOL CPDF_Parser::RebuildCrossRef() {
                       if (!pRoot ||
                           (pRef && IsValidObjectNumber(pRef->GetRefObjNum()) &&
                            m_ObjectInfo[pRef->GetRefObjNum()].pos != 0)) {
-                        for (const auto& it : *pTrailer) {
-                          const CFX_ByteString& key = it.first;
-                          CPDF_Object* pElement = it.second;
+                        auto it = pTrailer->begin();
+                        while (it != pTrailer->end()) {
+                          const CFX_ByteString& key = it->first;
+                          CPDF_Object* pElement = it->second;
+                          ++it;
                           FX_DWORD dwObjNum =
                               pElement ? pElement->GetObjNum() : 0;
                           if (dwObjNum) {