Land: Protect against a seg fault in CPDF_StructElementImpl constructor.

core/src/fpdfdoc/doc_tagged.cpp

Index: core/src/fpdfdoc/doc_tagged.cpp
diff --git a/core/src/fpdfdoc/doc_tagged.cpp b/core/src/fpdfdoc/doc_tagged.cpp
index 698157356c228fda50755f84945d36dbe4e038ab..c5fe39b6ee8b6cdc1344ded31d0295ecb4b38771 100644
--- a/core/src/fpdfdoc/doc_tagged.cpp
+++ b/core/src/fpdfdoc/doc_tagged.cpp
@@ -217,9 +217,11 @@ CPDF_StructElementImpl::CPDF_StructElementImpl(CPDF_StructTreeImpl* pTree, CPDF_
     m_pTree = pTree;
     m_pDict = pDict;
     m_Type = pDict->GetString(FX_BSTRC("S"));
-    CFX_ByteString mapped = pTree->m_pRoleMap->GetString(m_Type);
-    if (!mapped.IsEmpty()) {
-        m_Type = mapped;
+    if (pTree->m_pRoleMap) {
+        CFX_ByteString mapped = pTree->m_pRoleMap->GetString(m_Type);
+        if (!mapped.IsEmpty()) {
+            m_Type = mapped;
+        }
     }
     m_pParent = pParent;
     LoadKids(pDict);