[lldb] Fix use of null shared pointer (#10708)

(cherry-picked from commit 9765245)

Author: kastiglione

lldb/source/Plugins/Language/Swift/SwiftFormatters.cpp

@@ -1139,8 +1139,10 @@ class CheckedContinuationSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
           m_task_sp = ValueObject::CreateValueObjectFromAddress(
               "task", task_addr, m_backend.GetExecutionContextRef(),
               m_task_type, false);
-    if (auto synthetic_sp = m_task_sp->GetSyntheticValue())
-      m_task_sp = synthetic_sp;
+
+    if (m_task_sp)
+      if (auto synthetic_sp = m_task_sp->GetSyntheticValue())
+        m_task_sp = synthetic_sp;
     return ChildCacheState::eRefetch;
   }