8241296: Segfault in JNIHandleBlock::oops_do()

Reviewed-by: stefank, shade

src/hotspot/share/runtime/thread.cpp

@@ -867,7 +867,9 @@ bool Thread::claim_oops_do_par_case(int strong_roots_parity) {
 }
 
 void Thread::oops_do(OopClosure* f, CodeBlobClosure* cf) {
-  active_handles()->oops_do(f);
+  if (active_handles() != NULL) {
+    active_handles()->oops_do(f);
+  }
   // Do oop for ThreadShadow
   f->do_oop((oop*)&_pending_exception);
   handle_area()->oops_do(f);