Add a missing initialisation for CPDF_ContentMarkItem.

core/fpdfapi/fpdf_page/cpdf_contentmarkitem.cpp

Index: core/fpdfapi/fpdf_page/cpdf_contentmarkitem.cpp
diff --git a/core/fpdfapi/fpdf_page/cpdf_contentmarkitem.cpp b/core/fpdfapi/fpdf_page/cpdf_contentmarkitem.cpp
index 3b7a60c059af26d2c810da376d78134f53e88718..f44972568d37a81290f6581a7d7bd5d03eda3ca0 100644
--- a/core/fpdfapi/fpdf_page/cpdf_contentmarkitem.cpp
+++ b/core/fpdfapi/fpdf_page/cpdf_contentmarkitem.cpp
@@ -8,9 +8,8 @@
 
 #include "core/fpdfapi/fpdf_parser/include/cpdf_dictionary.h"
 
-CPDF_ContentMarkItem::CPDF_ContentMarkItem() {
-  m_ParamType = None;
-}
+CPDF_ContentMarkItem::CPDF_ContentMarkItem()
+    : m_ParamType(None), m_pParam(nullptr) {}
 
 CPDF_ContentMarkItem::CPDF_ContentMarkItem(const CPDF_ContentMarkItem& src) {
   m_MarkName = src.m_MarkName;