fix crashed in FXJSE_Value_Set

xfa/src/fxfa/src/parser/xfa_script_signaturepseudomodel.cpp

Index: xfa/src/fxfa/src/parser/xfa_script_signaturepseudomodel.cpp
diff --git a/xfa/src/fxfa/src/parser/xfa_script_signaturepseudomodel.cpp b/xfa/src/fxfa/src/parser/xfa_script_signaturepseudomodel.cpp
index cbaa86f0fd193b5239ce7ae336c892e49b0e9f34..b0f112ae9053d9bef48b1b332059b5993dc9554e 100644
--- a/xfa/src/fxfa/src/parser/xfa_script_signaturepseudomodel.cpp
+++ b/xfa/src/fxfa/src/parser/xfa_script_signaturepseudomodel.cpp
@@ -90,6 +90,8 @@ void CScript_SignaturePseudoModel::Script_SignaturePseudoModel_Enumerate(
   }
   IXFA_Doc* hDoc = pNotify->GetHDOC();
   CXFA_NodeList* pList = pNotify->GetDocProvider()->Enumerate(hDoc);
+  if (!pList)
+    return;
   FXJSE_Value_Set(pArguments->GetReturnValue(),
                   m_pDocument->GetScriptContext()->GetJSValueFromMap(pList));
 }