Hardening the vector iterator synthetic child(ren) provider against item-not-in-cluster asserts

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@178265 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/source/DataFormatters/CXXFormatterFunctions.cpp b/source/DataFormatters/CXXFormatterFunctions.cpp
index 20000a7..20231d9 100644
--- a/source/DataFormatters/CXXFormatterFunctions.cpp
+++ b/source/DataFormatters/CXXFormatterFunctions.cpp
@@ -958,6 +958,8 @@
 bool
 lldb_private::formatters::VectorIteratorSyntheticFrontEnd::Update()
 {
+    m_item_sp.reset();
+
     ValueObjectSP valobj_sp = m_backend.GetSP();
     if (!valobj_sp)
         return false;
@@ -975,7 +977,7 @@
     m_item_sp = ValueObject::CreateValueObjectFromAddress("item", item_ptr->GetValueAsUnsigned(0), m_exe_ctx_ref, ClangASTType(item_ptr->GetClangAST(),ClangASTType::GetPointeeType(item_ptr->GetClangType())));
     if (err.Fail())
         m_item_sp.reset();
-    return (m_item_sp.get() != NULL);
+    return false;
 }
 
 size_t