[LLDB] Fix for regression of test 'TestDataFormatterInvalidStdUniquePtr.py' introduced in r374195

Differential Revision: https://reviews.llvm.org/D68641

llvm-svn: 374231
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibStdcppUniquePointer.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibStdcppUniquePointer.cpp
index 84f9e57..cceb511 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibStdcppUniquePointer.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibStdcppUniquePointer.cpp
@@ -118,11 +118,11 @@
 
 lldb::ValueObjectSP
 LibStdcppUniquePtrSyntheticFrontEnd::GetChildAtIndex(size_t idx) {
-  if (idx == 0)
+  if (idx == 0 && m_ptr_obj)
     return m_ptr_obj->GetSP();
-  if (idx == 1)
+  if (idx == 1 && m_del_obj)
     return m_del_obj->GetSP();
-  if (idx == 2)
+  if (idx == 2 && m_obj_obj)
     return m_obj_obj->GetSP();
   return lldb::ValueObjectSP();
 }