Hardening in case a thread's frames are missing.

<rdar://problem/13254824>

llvm-svn: 175806
diff --git a/lldb/source/Expression/ClangExpressionDeclMap.cpp b/lldb/source/Expression/ClangExpressionDeclMap.cpp
index 92dfbef..1214db3 100644
--- a/lldb/source/Expression/ClangExpressionDeclMap.cpp
+++ b/lldb/source/Expression/ClangExpressionDeclMap.cpp
@@ -82,7 +82,7 @@
     Target *target = exe_ctx.GetTargetPtr();
     if (exe_ctx.GetFramePtr())
         m_parser_vars->m_sym_ctx = exe_ctx.GetFramePtr()->GetSymbolContext(lldb::eSymbolContextEverything);
-    else if (exe_ctx.GetThreadPtr())
+    else if (exe_ctx.GetThreadPtr() && exe_ctx.GetThreadPtr()->GetStackFrameAtIndex(0))
         m_parser_vars->m_sym_ctx = exe_ctx.GetThreadPtr()->GetStackFrameAtIndex(0)->GetSymbolContext(lldb::eSymbolContextEverything);
     else if (exe_ctx.GetProcessPtr())
     {