Add a defensive check for nullptr as in the block above.

Unfortunately I had to work backwards from a crash log,
so I don't have a good testcase at this point in time.

rdar://problem/51874647

llvm-svn: 364344
diff --git a/lldb/source/Target/CPPLanguageRuntime.cpp b/lldb/source/Target/CPPLanguageRuntime.cpp
index 836523a..8e503bd 100644
--- a/lldb/source/Target/CPPLanguageRuntime.cpp
+++ b/lldb/source/Target/CPPLanguageRuntime.cpp
@@ -280,7 +280,7 @@
   }
 
   // Case 4 or 5
-  if (!symbol->GetName().GetStringRef().startswith("vtable for")) {
+  if (symbol && !symbol->GetName().GetStringRef().startswith("vtable for")) {
     optional_info.callable_case =
         LibCppStdFunctionCallableCase::FreeOrMemberFunction;
     optional_info.callable_address = function_address_resolved;