Fix a null object bug

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 926117722f7d93eb63a1cbe33e9c4a13ce6b98f6..b79aad6f237147d96c60f0dafdc8efd57cc1ee37 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
@@ -1211,7 +1211,7 @@ CPDF_StreamAcc* CPDF_Parser::GetObjectStream(FX_DWORD objnum)
     if (m_ObjectStreamMap.Lookup((void*)(FX_UINTPTR)objnum, (void*&)pStreamAcc)) {
         return pStreamAcc;
     }
-    const CPDF_Stream* pStream = (CPDF_Stream*)m_pDocument->GetIndirectObject(objnum);
+    const CPDF_Stream* pStream = m_pDocument ? (CPDF_Stream*)m_pDocument->GetIndirectObject(objnum) : NULL;
     if (pStream == NULL || pStream->GetType() != PDFOBJ_STREAM) {
         return NULL;
     }