Null CPDF_CountedObj::m_pObj prior to deletion

core/fpdfapi/fpdf_page/cpdf_countedobject.h

Index: core/fpdfapi/fpdf_page/cpdf_countedobject.h
diff --git a/core/fpdfapi/fpdf_page/cpdf_countedobject.h b/core/fpdfapi/fpdf_page/cpdf_countedobject.h
index e7f4ab6af0efe8375919264580d429a7a6185ae8..c61e02458917c6b7f54004530d71154685389b91 100644
--- a/core/fpdfapi/fpdf_page/cpdf_countedobject.h
+++ b/core/fpdfapi/fpdf_page/cpdf_countedobject.h
@@ -20,8 +20,10 @@ class CPDF_CountedObject {
     m_pObj = ptr;
   }
   void clear() {  // Now you're all weak ptrs ...
-    delete m_pObj;
+    // Guard against accidental re-entry.
+    T* pObj = m_pObj;
     m_pObj = nullptr;
+    delete pObj;
   }
   T* get() const { return m_pObj; }
   T* AddRef() {